extdiff: correctly handle deleted subrepositories (issue3153) Previously, when extdiff was called on two changesets where a subrepository had been removed, an unexpected KeyError would be raised. Now, the missing subrepository will be ignored. This behavior mirrors the behavior in diffordiffstat from cmdutil.py line ~1138-1153. The KeyError is caught and the revision is set to None. try/catch of LookupError around matchmod.narrowmatcher and sub.status is removed, as LookupError is not raised anywhere within those methods or deeper calls.