Fix parse error message/details output.

Author: BigBlueHat

playground/next/index.html

@@ -270,9 +270,9 @@ <h2 class="ui massive header">JSON-LD Playground</h2>
     </div>
   </div>
   <!-- errors -->
-  <div class="ui error message" v-show="parseError">
+  <div class="ui error message" v-show="parseError.message">
     <div class="header" v-text="parseError.message"></div>
-    <div class="content" v-if="parseError.details">
+    <div class="content" v-if="parseError && parseError?.details?.event">
       <pre v-text="JSON.stringify(parseError.details.event, null, 2)"></pre>
     </div>
   </div>