mshtml: Release event target in XMLHttpRequest destructor.

dlls/mshtml/xmlhttprequest.c

@@ -252,6 +252,7 @@ static ULONG WINAPI HTMLXMLHttpRequest_Release(IHTMLXMLHttpRequest *iface)
     if(!ref) {
         if(This->event_listener)
             detach_xhr_event_listener(This->event_listener);
+        release_event_target(&This->event_target);
         release_dispex(&This->event_target.dispex);
         nsIXMLHttpRequest_Release(This->nsxhr);
         heap_free(This);