Bug 605760 - Deal with null a subject principal here. r=jst

--HG--
extra : transplant_source : %BF%E0aY%BB/K%D7Xf%DD%60%FB%B0%DB%1B%C5%B1%8C%AA

js/src/xpconnect/wrappers/AccessCheck.cpp

@@ -247,6 +247,9 @@ AccessCheck::documentDomainMakesSameOrigin(JSContext *cx, JSObject *obj)
         subject = GetPrincipal(JS_GetGlobalForObject(cx, scope));
     }
 
+    if (!subject)
+        return false;
+
     {
         JSAutoEnterCompartment ac;