check if topicData is valid

src/webserver.js

@@ -224,8 +224,10 @@ var express = require('express'),
 			async.waterfall([
 				function(next) {
 					topics.getTopicWithPosts(tid, ((req.user) ? req.user.uid : 0), function(err, topicData) {
+						if(topicData) {
 							if(topicData.deleted === '1' && topicData.expose_tools === 0)
 								return next(new Error('Topic deleted'), null);
+						}
 
 						next(err, topicData);
 					});