Don't allow dynamic properties on generators

Noticed this because we leak those properties in GC. This was
never intended to be allowed.

Author: nikic

Zend/tests/generators/dynamic_properties.phpt

@@ -0,0 +1,19 @@
+--TEST--
+It's not possible to assign dynamic properties on a generator
+--FILE--
+<?php
+
+function gen() {
+    yield;
+}
+
+$gen = gen();
+try {
+    $gen->prop = 42;
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+
+?>
+--EXPECT--
+Cannot create dynamic property Generator::$prop

Zend/zend_generators.c

@@ -1159,7 +1159,7 @@ void zend_register_generator_ce(void) /* {{{ */
 
 	INIT_CLASS_ENTRY(ce, "Generator", class_Generator_methods);
 	zend_ce_generator = zend_register_internal_class(&ce);
-	zend_ce_generator->ce_flags |= ZEND_ACC_FINAL;
+	zend_ce_generator->ce_flags |= ZEND_ACC_FINAL | ZEND_ACC_NO_DYNAMIC_PROPERTIES;
 	zend_ce_generator->create_object = zend_generator_create;
 	zend_ce_generator->serialize = zend_class_serialize_deny;
 	zend_ce_generator->unserialize = zend_class_unserialize_deny;