Bug 1097597 - Check if there is a Loop toolbarbutton node in updateToolbarState. r=Standard8

--HG--
extra : rebase_source : b248a35f2e218900e9e0dc7481d36454949d14be

browser/base/content/browser-loop.js

@@ -74,6 +74,9 @@ XPCOMUtils.defineLazyModuleGetter(this, "PanelFrame", "resource:///modules/Panel
      *                   temporarily shown until the next state change.
      */
     updateToolbarState: function(aReason = null) {
+      if (!this.toolbarButton.node) {
+        return;
+      }
       let state = "";
       if (MozLoopService.errors.size) {
         state = "error";