Fix missing addref for __unset

Fixes GH-21603
Closes GH-21604

Author: iluuu1994

NEWS

@@ -10,6 +10,7 @@ PHP                                                                        NEWS
   . Fixed bug GH-21605 (Missing addref for Countable::count()). (ilutov)
   . Fixed bug GH-21699 (Assertion failure in shutdown_executor when resolving
     self::/parent::/static:: callables if the error handler throws). (macoaure)
+  . Fixed bug GH-21603 (Missing addref for __unset). (ilutov)
 
 - Curl:
   . Add support for brotli and zstd on Windows. (Shivam Mathur)

Zend/tests/gh21603.phpt

@@ -0,0 +1,22 @@
+--TEST--
+GH-21603: Missing addref for __unset
+--CREDITS--
+cnwangjihe
+--FILE--
+<?php
+
+class C {
+    public function __unset($name) {
+        global $c;
+        $c = null;
+        var_dump($this);
+    }
+}
+
+$c = new C;
+unset($c->prop);
+
+?>
+--EXPECTF--
+object(C)#%d (0) {
+}

Zend/zend_object_handlers.c

@@ -1653,9 +1653,11 @@ ZEND_API void zend_std_unset_property(zend_object *zobj, zend_string *name, void
 		}
 		if (!((*guard) & IN_UNSET)) {
 			/* have unsetter - try with it! */
+			GC_ADDREF(zobj);
 			(*guard) |= IN_UNSET; /* prevent circular unsetting */
 			zend_std_call_unsetter(zobj, name);
 			(*guard) &= ~IN_UNSET;
+			OBJ_RELEASE(zobj);
 			return;
 		} else if (UNEXPECTED(IS_WRONG_PROPERTY_OFFSET(property_offset))) {
 			/* Trigger the correct error */