Properly check for IS_UNDEF when optimizing

Author: TysonAndre

ext/opcache/Optimizer/dfa_pass.c

@@ -448,7 +448,8 @@ int zend_dfa_optimize_calls(zend_op_array *op_array, zend_ssa *ssa)
 							ssa_op->op1_use_chain = var->use_chain;
 							var->use_chain = op_num;
 						}
-						if (zend_hash_num_elements(src) == 0) {
+						if (zend_hash_num_elements(src) == 0 &&
+							!(ssa->var_info[ssa_op->op1_use].type & MAY_BE_UNDEF)) {
 							/* TODO remove needle from the uses of ssa graph? */
 							ZVAL_FALSE(&tmp);
 							zend_array_destroy(dst);