xfs: do not use unchecked extent indices in xfs_bunmapi
Make sure to only call xfs_iext_get_ext after we've validate the
extent index when moving on to the next index in xfs_bunmapi. Also
remove the old workaround for too large indices that has been
superceeded by the proper fix in xfs_bmap_del_extent.
Based on an earlier patch from Lachlan McIlroy.
Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Lachlan McIlroy <lmcilroy@redhat.com> Signed-off-by: Alex Elder <aelder@sgi.com>