dumb: Handle missing or corrupted pack file
Some dumb git servers might reference a no longer existing pack file while it is possible to fully load a repository without it.
See for instance https://git.zap.org.au/git/console-fonts-utils.git/objects/info/packs and https://git.zap.org.au/git/console-fonts-utils.git/objects/pack/.
So remove bogus pack file from the global packs list when encountering such edge case and try to continue the loading anyway.
Related to #3618 (closed)
Migrated from D6416 (view on Phabricator)