Ensure that form is not disposed.
revisions[0].ParentGuids was accessed without ensuring that revision.Count > 0

(cherry picked from commit d8c44e1cc7acb25f03a8c95272c17702a17a95cb)
Merge branch 'release/2.47' into release/2.48

Conflicts:
	GitUI/CommandsDialogs/BrowseDialog/FormUpdates.cs