fix display of fiddles that DON'T have compile errors

experimental/webtry/res/js/webtry.js

 /**
  * Common JS that talks XHR back to the server and runs the code and receives
  * the results.
  */
 
 
 /**
  * All the functionality is wrapped up in this anonymous closure, but we need
  * to be told if we are on the workspace page or a normal try page, so the
  * workspaceName is passed into the closure, it must be set in the global
@@ skipping 251 matching lines @@
         // The response is JSON of the form:
         // {
         //   "message": "you had an error...",
         //   "img": "<base64 encoded image but only on success>"
         // }
         //
         // The img is optional and only appears if there is a valid
         // image to display.
         endWait();
         body = JSON.parse(e.target.response);
-        if (body.compileErrors.length) {
+        if (null != body.compileErrors && body.compileErrors.length) {
           html = "";
           for (i = 0 ; i < body.compileErrors.length ; i++) {
             compileError = body.compileErrors[i];
 
             err = document.createElement("div");
             err.className = "compile-error";
 
             loc = document.createElement("span");
             loc.className = "error-location";
             loc.innerHTML = "Line " + compileError.line + ", col " + compileError.column + ": ";
@@ skipping 85 matching lines @@
     }
 
     // If loaded via HTML Imports then DOMContentLoaded will be long done.
     if (document.readyState != "loading") {
       onLoad();
     } else {
       this.addEventListener('load', onLoad);
     }
 
 })();