xfs_repair: always release btree buffers when refcountbt checks fail

xfs_repair: always release btree buffers when refcountbt checks fail

During phase 4 of repair, we compare the refcount records we've computed
against what's in the refcount btree.  If the btree is corrupt the
libxfs refcount calls will fail, but on our way out of the function we
don't make sure to clear all the btree cursor's buffer pointers.  This
leads to a repair deadlock in xfs/372 when fuzzing ptrs[1] to -1U
because we forgot to release a buffer.

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