repair: check ino alignment value to avoid mod by zero

repair: check ino alignment value to avoid mod by zero

xfs_repair checks inode records for valid alignment according to the
alignment specified in the superblock. It currently performs the
alignment check whenever fs_aligned_inodes is set, which is determined
based on whether the fs supports the field.

Support for the field does not guarantee its value is non-zero, however.
For example, a large block size fs on a large page size arch (e.g.,
ppc64):

	mkfs.xfs -f -m crc=1,finobt=1 -b size=64k <dev>

... can lead to incorrect badly aligned inode record messages from
xfs_repair and other problems.

Update the inobt and finobt checks to verify that alignment is a
non-zero value before attempting to use it to divide (mod) by zero.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>