xfs_db: set b_ops to NULL in set_cur for types without verifiers

xfs_db: set b_ops to NULL in set_cur for types without verifiers

If we are using set_cur() to set a type that has no verifier ops,
be sure to set b_ops to NULL so that the old verifiers don't run
against the buffer anymore, which may have changed size.

Fixes: cdabe556 ("xfs_db: consolidate set_iocur_type behavior")
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>