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().

Reported by:  crypt47, nvass
Fix by:       Robert Wing
Tested by:    Robert Wing
PR:           255030
PR:           255979
MFC after:    3 days
Sponsored by: Netflix

sbin/fsck_ffs/main.c

@@ -272,6 +272,7 @@ checkfilesys(char *filesys)
 	 * exit status will cause a foreground check to be run.
 	 */
 	sblock_init();
+	bufinit();
 	if (bkgrdcheck) {
 		if ((fsreadfd = open(filesys, O_RDONLY)) < 0 || readsb(0) == 0)
 			exit(3);	/* Cannot read superblock */

sbin/fsck_ffs/setup.c

@@ -298,7 +298,6 @@ setup(char *dev)
 		    (uintmax_t)numdirs * sizeof(struct inoinfo *));
 		goto badsb;
 	}
-	bufinit();
 	if (sblock.fs_flags & FS_DOSOFTDEP)
 		usedsoftdep = 1;
 	else