UI: Fix case where cef func may not be present

Due to a particular... plugin we all know and love, the new
QCefWidget::executeJavascript() function may not actually be present as
it should be. So, we have to verify that it's available, and only use it
in that case.

UI/window-basic-settings.cpp

@@ -4248,7 +4248,7 @@ void OBSBasicSettings::on_listWidget_itemSelectionChanged()
 void OBSBasicSettings::UpdateYouTubeAppDockSettings()
 {
 #if defined(BROWSER_ENABLED) && defined(YOUTUBE_ENABLED)
-	if (cef) {
+	if (cef_js_avail) {
 		std::string service = ui->service->currentText().toStdString();
 		if (IsYouTubeService(service)) {
 			if (!main->GetYouTubeAppDock()) {