Don't pop up errors from a refresh worker once the repo was switched

An error returned from a gocui worker is shown to the user in an error
popup. For the branch loader's behind-counts worker that used to be the
"no such ref" popup when a background refresh crossed a repo switch:
the old repo's main branch didn't exist in the new repo. The previous
commits fix that scenario properly — the command now runs against the
repo the refresh was started for — but a stale worker can still fail
legitimately, most plausibly because that repo was deleted after
switching away from it (e.g. removing a worktree). Its results are
dropped anyway, so log the error instead of alarming the user about a
repo they already left.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pkg/gui/controllers/helpers/refresh_helper.go

@@ -1039,7 +1039,18 @@ func (self *RefreshHelper) refreshBranches(captured capturedBranchState, refresh
 		loadBehindCounts,
 		func(f func() error) {
 			self.onWorker(env.background, func(_ gocui.Task) error {
-				return f()
+				err := f()
+				if err != nil && self.c.State().GetRepoGeneration() != env.generation {
+					// An error returned from a worker is shown in a popup. Don't
+					// do that if the repo was switched while this worker was in
+					// flight: its results are dropped anyway, and the error
+					// concerns a repo the user has already left — e.g. failing to
+					// compute the behind-counts for a worktree that was deleted
+					// after switching away from it.
+					self.c.Log.Warnf("dropping error from a stale refresh worker after a repo switch: %v", err)
+					return nil
+				}
+				return err
 			})
 		},
 		func() {