Avoid NPE

Author: janodvarko

lib/inspector-overlay.js

@@ -284,6 +284,10 @@ const InspectorOverlay = Class(
 
   onDataModified: function(nodeData, hasJQueryData) {
     let markupView = this.panel.markup;
+    if (!markupView) {
+      return;
+    }
+
     let client = this.toolbox.target.client;
     let nodeFront = nodeData.node;