convert: don't drop commits that are empty in the source when using --filemap I ran into this when using `hg lfconvert --to-normal` (which uses the filemap class internally), and saw that commits with nothing but a branch change were dropped. We could put in an option that only lfconvert uses internally. But silently dropping anything other than a commit where all changes were excluded seems unintended. For example, there's a message in mercurial_sink.putcommit() if it drops an empty commit. (And the reason that isn't kicking in here is because lfconvert isn't passing --filemap, so the self.filemapmode conditional there is always False.) The naive change of `return not files` broke test-convert-filemap.t, so this is a little more elaborate than needed for converting from largefiles.