udf: Allow volume descriptor sequence to be terminated by unrecorded block

According to ECMA-167 3/8.4.2 a volume descriptor sequence can be
terminated also by an unrecorded block within the extent of volume
descriptor sequence. Currently we errored out in such case making such
volumes unmountable. Handle that case by treating any invalid block as a
block terminating the sequence.
Reported-by: Pali Rohár <pali.rohar@gmail.com>
Acked-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/super.c

@@ -1627,12 +1627,8 @@ static noinline int udf_process_sequence(
 	for (; (!done && block <= lastblock); block++) {
 
 		bh = udf_read_tagged(sb, block, block, &ident);
-		if (!bh) {
-			udf_err(sb,
-				"Block %llu of volume descriptor sequence is corrupted or we could not read it\n",
-				(unsigned long long)block);
-			return -EAGAIN;
-		}
+		if (!bh)
+			break;
 
 		/* Process each descriptor (ISO 13346 3/8.3-8.4) */
 		gd = (struct generic_desc *)bh->b_data;