Do not increment undefined mapview stat tags

lib/cartodb/carto_data.js

@@ -69,6 +69,7 @@ module.exports = function() {
           },
           function incrementTag(err, val) {
             if ( err ) throw err;
+            if ( _.isUndefined(stat_tag) ) return 1;
             redisKey = _.template(that.tagged_mapview_key, {username: username, stat_tag: stat_tag});
             that.redisCmd(me.user_metadata_db, 'ZINCRBY', [redisKey, 1, now], this);
           },