[skip ci] Fix uninitialized fn_flags2 for internal functions

This field is still unused on master, but required for GH-19941.

Author: iluuu1994

Zend/zend_API.c

@@ -3045,6 +3045,7 @@ ZEND_API zend_result zend_register_functions(zend_class_entry *scope, const zend
 		internal_function->prop_info = NULL;
 		internal_function->attributes = NULL;
 		internal_function->frameless_function_infos = ptr->frameless_function_infos;
+		internal_function->fn_flags2 = 0;
 		if (EG(active)) { // at run-time: this ought to only happen if registered with dl() or somehow temporarily at runtime
 			ZEND_MAP_PTR_INIT(internal_function->run_time_cache, zend_arena_calloc(&CG(arena), 1, zend_internal_run_time_cache_reserved_size()));
 		} else {