Fix over-eager named params optimization

We can't relax a named param to a positional param if we encountered
any unknown parameters in the meantime.

Author: nikic

Zend/tests/named_params/unknown_named_param.phpt

@@ -15,6 +15,12 @@ try {
     echo $e->getMessage(), "\n";
 }
 
+try {
+    test(b: 2, a: 1);
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+
 try {
     test2(a: 42);
 } catch (Error $e) {
@@ -24,3 +30,4 @@ try {
 ?>
 --EXPECT--
 Unknown named parameter $b
+Unknown named parameter $b

Zend/zend_compile.c

@@ -3369,7 +3369,7 @@ uint32_t zend_compile_args(
 
 			if (fbc) {
 				arg_num = zend_get_arg_num(fbc, arg_name);
-				if (arg_num == arg_count + 1) {
+				if (arg_num == arg_count + 1 && !may_have_undef) {
 					/* Using named arguments, but passing in order. */
 					arg_name = NULL;
 					arg_count++;