在用户剔重逻辑中增加from非空判断，防止异常数据导致执行错误。

app/service/forumThreadService.js

@@ -1017,7 +1017,7 @@ function getMobileSubThreads(doc, sort, callback) {
                 _.forEach(docs, function(one, i) {
                     var flag = true;
                     _.forEach(list, function(two, k) {
-                        if(one.from._id == two.from._id){
+                        if(one.from && two.from && one.from._id == two.from._id){
                             flag = false;
                         }
                     });