Store empty (default) branch in branch cache, too.
Operations on this branch don't work otherwise.
Reading branches.cache had to be adjusted to allow an empty label.
Adjusted reading of the cache tip for symmetry, no functional change here.
uisetup called
ui.parentui is None
reposetup called for a
ui == repo.ui
Foo
uisetup called
ui.parentui is None
reposetup called for a
ui == repo.ui
reposetup called for b
ui == repo.ui
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
uisetup called
ui.parentui is None
Bar