Fix fsck_ufs segfaults with gjournal (SU+J)
The segfault was being hit in ckfini() (sbin/fsck_ffs/fsutil.c)
while attempting to traverse the buffer cache to flush dirty buffers.
The tail queue used for the buffer cache was not initialized before
dropping into gjournal_check(). Move the buffer initialization earlier
so that it has been done before calling gjournal_check().