Scope

• If there is no default branch for the pipeline we should not show the favourite star
• If favoriting fails for whatever reason, the favourite star should not change state

Problem
While creating a set of example screenshots, I noticed that the web UI had the Favorite star icon enabled, so I clicked it.

Turns out you can't do that. Oops.

I think it would be an improvement to grey out or disable icons which are not avaialble for the current view context.