Bug #50942 mix_innodb_myisam_side_effects.test is not deterministic

The test was used to fail because of 
 UPDATE t3,t4 SET t3.a=t4.a + bug27417(1);
did not prescribe the order of two row operations implied by the update.

Fixed with forcing the order with adding a where condition w/o
affecting the former bug fixes logics.

mysql-test/extra/binlog_tests/mix_innodb_myisam_side_effects.test

@@ -214,7 +214,7 @@ CREATE TABLE t5 (a int, PRIMARY KEY (a)) ENGINE=InnoDB;
 
 # execute
  --error ER_DUP_ENTRY
- UPDATE t3,t4 SET t3.a=t4.a + bug27417(1);
+ UPDATE t3,t4 SET t3.a = t4.a + bug27417(1) where t3.a = 1;
 
 # check
  select count(*) from t1 /* must be 1 */;