Set the return value to 'undefined' on an unexpected error (since we always use a callback); improve comments

Author: adamstallard

lib/vows/suite.js

@@ -129,12 +129,14 @@ this.Suite.prototype = new(function () {
                 }
 
                 // Run the topic, passing the previous context topics
-                // If topic `throw`s an exception, pass it down as a value
                 try {
                     topic = topic.apply(ctx.env, ctx.topics);
                 }
+                // If an unexpected error occurs in the topic, set the return
+                // value to 'undefined' and call back with the error
                 catch (ex) {
                     ctx.env.callback(ex);
+                    topic = undefined;
                 }
 
                 if (typeof(topic) === 'undefined') { ctx._callback = true }