xfs_repair: don't assert on bad '.' entry in no-modify mode

xfs_repair: don't assert on bad '.' entry in no-modify mode

During phase 3, we check the '.' entry of a directory inode and (in
modify mode) zap it if the name isn't valid.  During phase 6, we assert
that the '.' entry now reflects the correct name.  In no-modify mode
this is incorrect because we didn't actually fix anything, so repair
asserts and crashes.

Found by fuzzing bu[0].namelen = 4 in xfs/387 and running xfs_repair -n.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>