Similar to JENKINS-25897

In a freestyle project,
enter a cron with an illegal date like 0 0 31 6 *
When saving or moving focus out of the entry box it will create a thread at 100% cpu.
A new thread will be created each time, after saving, that you try to configure this job.

Tested on LTS 1.651.3 ?
2.45

Handling GET /job/xxxxxxxxxx/descriptorByName/hudson.triggers.TimerTrigger/checkSpec from 127.0.0.1 : RequestHandlerThread5
java.util.GregorianCalendar.add(Unknown Source)
hudson.scheduler.CronTab$CalendarField$3.rollUp(CronTab.java:270)
hudson.scheduler.CronTab.floor(CronTab.java:396)
hudson.scheduler.CronTabList.previous(CronTabList.java:134)
hudson.triggers.TimerTrigger$DescriptorImpl.updateValidationsForNextRun(TimerTrigger.java:106)
hudson.triggers.TimerTrigger$DescriptorImpl.doCheckSpec(TimerTrigger.java:91)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
java.lang.reflect.Method.invoke(Unknown Source)
org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:320)
org.kohsuke.stapler.Function.bindAndInvoke(Function.java:163)
org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:96)
org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:124)
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:58)
org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
org.kohsuke.stapler.MetaClass$5.doDispatch(MetaClass.java:233)
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:58)
org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
org.kohsuke.stapler.MetaClass$5.doDispatch(MetaClass.java:233)
org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:58)
org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
org.kohsuke.stapler.Stapler.invoke(Stapler.java:649)
org.kohsuke.stapler.Stapler.service(Stapler.java:238)
javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:812)
org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1669)
hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:135)
com.smartcodeltd.jenkinsci.plugin.assetbundler.filters.LessCSS.doFilter(LessCSS.java:47)
hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:132)
net.bull.javamelody.MonitoringFilter.doFilter(MonitoringFilter.java:201)
net.bull.javamelody.MonitoringFilter.doFilter(MonitoringFilter.java:178)
net.bull.javamelody.PluginMonitoringFilter.doFilter(PluginMonitoringFilter.java:85)
org.jvnet.hudson.plugins.monitoring.HudsonMonitoringFilter.doFilter(HudsonMonitoringFilter.java:102)
hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:132)
hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:126)
org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652)
hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:49)
org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
hudson.security.UnwrapSecurityExceptionFilter.doFilter(UnwrapSecurityExceptionFilter.java:51)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
jenkins.security.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:117)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
org.acegisecurity.providers.anonymous.AnonymousProcessingFilter.doFilter(AnonymousProcessingFilter.java:125)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
org.acegisecurity.ui.rememberme.RememberMeProcessingFilter.doFilter(RememberMeProcessingFilter.java:142)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
org.acegisecurity.ui.AbstractProcessingFilter.doFilter(AbstractProcessingFilter.java:271)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
jenkins.security.BasicHeaderProcessor.doFilter(BasicHeaderProcessor.java:93)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
org.acegisecurity.context.HttpSessionContextIntegrationFilter.doFilter(HttpSessionContextIntegrationFilter.java:249)
hudson.security.HttpSessionContextIntegrationFilter2.doFilter(HttpSessionContextIntegrationFilter2.java:67)
hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
hudson.security.HudsonFilter.doFilter(HudsonFilter.java:171)
org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652)
org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:49)
org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652)
hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:81)
org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652)
org.kohsuke.stapler.DiagnosticThreadNameFilter.doFilter(DiagnosticThreadNameFilter.java:30)
org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652)
org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:585)
org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:553)
org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:223)
org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1127)
org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:515)
org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185)
org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1061)
org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:97)
org.eclipse.jetty.server.Server.handle(Server.java:499)
org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:311)
org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:257)
org.eclipse.jetty.io.AbstractConnection$2.run(AbstractConnection.java:544)
winstone.BoundedExecutorService$1.run(BoundedExecutorService.java:77)
java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
java.lang.Thread.run(Unknown Source)