xfs_repair: initialize realloced bplist in longform_dir2_entry_check

xfs_repair: initialize realloced bplist in longform_dir2_entry_check

If we need to realloc the bplist[] array holding buffers for a given
directory, we don't initialize the new slots.  This causes a problem
if the directory has holes, because those slots never get filled in.

At the end of the function we call libxfs_putbuf for every non-null
slot, and any uninitialized slots are segfault landmines.

Make sure we initialize all new slots to NULL for this reason.

Reported-by: Oleg Davydov <burunduk3@gmail.com>
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>