xfs: BMAPX shouldn't barf on inline-format directories

When we're fulfilling a BMAPX request, jump out early if the data fork
is in local format.  This prevents us from hitting a debugging check in
bmapi_read and barfing errors back to userspace.  The on-disk extent
count check later isn't sufficient for IF_DELALLOC mode because da
extents are in memory and not on disk.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>