branches/5.1: row_unlock_for_mysql(): When the clustered index is unknown,

refuse to unlock the record.
(Bug #45357, caused by the fix of Bug #39320).
rb://132 approved by Sunny Bains.

mysql-test/innodb_bug45357.result

+set session transaction isolation level read committed;
+create table bug45357(a int, b int,key(b))engine=innodb;
+insert into bug45357 values (25170,6122);
+update bug45357 set a=1 where b=30131;
+delete from bug45357 where b < 20996;
+delete from bug45357 where b < 7001;
+drop table bug45357;

mysql-test/innodb_bug45357.test

+-- source include/have_innodb.inc
+
+set session transaction isolation level read committed;
+
+create table bug45357(a int, b int,key(b))engine=innodb;
+insert into bug45357 values (25170,6122);
+update bug45357 set a=1 where b=30131;
+delete from bug45357 where b < 20996;
+delete from bug45357 where b < 7001;
+drop table bug45357;

row/row0mysql.c

@@ -1529,9 +1529,14 @@ row_unlock_for_mysql(
 			index = btr_pcur_get_btr_cur(clust_pcur)->index;
 		}
 
+		if (UNIV_UNLIKELY(!(index->type & DICT_CLUSTERED))) {
+			/* This is not a clustered index record.  We
+			do not know how to unlock the record. */
+			goto no_unlock;
+		}
+
 		/* If the record has been modified by this
 		transaction, do not unlock it. */
-		ut_a(index->type & DICT_CLUSTERED);
 
 		if (index->trx_id_offset) {
 			rec_trx_id = trx_read_trx_id(rec
@@ -1568,7 +1573,7 @@ row_unlock_for_mysql(
 						prebuilt->select_lock_type);
 			}
 		}
-
+no_unlock:
 		mtr_commit(&mtr);
 	}