fix for PHP 7.4

Author: hrissan

vkext/vk_zend.h

@@ -239,8 +239,9 @@ static zend_always_inline void vk_zend_call_known_instance_method(zval *object,
 #if PHP_MAJOR_VERSION >= 8
   zend_call_known_instance_method(fun, zobj, retval_ptr, param_count, params);
 #else
-  // TODO - this branch is not tested yet
-  zend_call_known_instance_method(fun, object, retval_ptr, param_count, params);
+  zval method_name_zval;
+  ZVAL_STR(&method_name_zval, method_name);
+  call_user_function(NULL, object, &method_name_zval, retval_ptr, param_count, params);
 #endif
 }