Bug 936604, null check event handler in event listener service, r=bz

dom/events/nsEventListenerService.cpp

@@ -94,7 +94,7 @@ nsEventListenerInfo::GetJSVal(JSContext* aCx,
   }
 
   nsCOMPtr<nsIJSEventListener> jsl = do_QueryInterface(mListener);
-  if (jsl) {
+  if (jsl && jsl->GetHandler().HasEventHandler()) {
     JS::Handle<JSObject*> handler(jsl->GetHandler().Ptr()->Callable());
     if (handler) {
       aAc.construct(aCx, handler);

dom/events/test/test_bug448602.html

@@ -60,6 +60,14 @@ function runTests() {
   is(jsdvalue.jsType, 3, "Event listener should be a function! (1)");
 */
 
+  root.removeAttribute("onclick");
+  root.setAttribute("onclick", "...invalid script...");
+  SimpleTest.expectUncaughtException(true);
+  infos = els.getListenerInfoFor(root, {});
+  SimpleTest.expectUncaughtException(false);
+  is(infos.length, 1);
+  is(infos[0].listenerObject, null);
+
   root.removeAttribute("onclick");
   infos = els.getListenerInfoFor(root, {});
   is(infos.length, 0, "Element shouldn't have listeners (2)");