patch: fix patchmeta/hunk synchronization in iterhunks() Synchronizing on bfile does not work on file removal where bfile is /dev/null. We match items on afile or bfile instead. The incorrect code makes iterhunks() to emit patchmeta and hunks separately in some cases. This is currently hidden by applydiff() being too tolerant when processing patchmeta, and will be fixed later.