MDEV-18945 Assertion `fixed == 1' failed in Item_cond_and::val_int

In the function make_cond_for_table_from_pred a call of ix_fields()
missed checking of the return code. As a result an extracted constant
condition could be not well formed and this caused an assertion failure.

mysql-test/r/update.result

@@ -719,3 +719,16 @@ Handler_read_rnd_deleted	0
 Handler_read_rnd_next	0
 drop table t1, t2;
 # End of MariaDB 10.0 tests
+#
+# MDEV-18945: multi-table update with constant table and
+#             comparison of date field with integer field
+#
+CREATE TABLE t1 (i1 int, d1 date , i2 int , d2 date) engine=myisam;
+INSERT INTO t1 VALUES (19,'0000-00-00',73,'2008-05-21');
+CREATE TABLE t2 (d1 date , i1 int, i2 int , d2 date) engine=myisam;
+INSERT INTO t2 VALUES
+('2006-01-12',-102,45,'2023-11-25'),('2034-12-19',-102,45,'2001-11-20');
+UPDATE t1,t2 SET t1.i1 = -39 WHERE t2.d1 <> t1.i1 AND t2.d1 = t1.d2;
+ERROR 22007: Incorrect datetime value: '19' for column `test`.`t1`.`i1` at row 1
+DROP TABLE t1,t2;
+# End of MariaDB 10.2 tests

mysql-test/t/update.test

@@ -654,3 +654,22 @@ show status like 'Handler_read%';
 drop table t1, t2;
 
 --echo # End of MariaDB 10.0 tests
+
+--echo #
+--echo # MDEV-18945: multi-table update with constant table and
+--echo #             comparison of date field with integer field
+--echo #
+
+CREATE TABLE t1 (i1 int, d1 date , i2 int , d2 date) engine=myisam;
+INSERT INTO t1 VALUES (19,'0000-00-00',73,'2008-05-21');
+
+CREATE TABLE t2 (d1 date , i1 int, i2 int , d2 date) engine=myisam;
+INSERT INTO t2 VALUES
+  ('2006-01-12',-102,45,'2023-11-25'),('2034-12-19',-102,45,'2001-11-20');
+
+--error ER_TRUNCATED_WRONG_VALUE
+UPDATE t1,t2 SET t1.i1 = -39 WHERE t2.d1 <> t1.i1 AND t2.d1 = t1.d2;
+
+DROP TABLE t1,t2;
+
+--echo # End of MariaDB 10.2 tests

sql/sql_select.cc

@@ -20614,7 +20614,8 @@ make_cond_for_table_from_pred(THD *thd, Item *root_cond, Item *cond,
           the new parent Item. This should not be expensive because all
 	  children of Item_cond_and should be fixed by now.
 	*/
-	new_cond->fix_fields(thd, 0);
+	if (new_cond->fix_fields(thd, 0))
+          return (COND*) 0;
 	new_cond->used_tables_cache=
 	  ((Item_cond_and*) cond)->used_tables_cache &
 	  tables;