localrepo: extract handling of some special value in __getitem__...
localrepo: extract handling of some special value in __getitem__
The value "tip" should always be accessible, otherwise there is some problematic
bug in the lower level. So we can access this outside of the general try/catch.
If it fails some wider and actual big is in play.
Differential Revision:
https://phab.mercurial-scm.org/D7475