fix(uiSelectMultipleDirective): fix track by error

Fixed error when accessing length property on undefined for propsItemNameMatches and matches

Closes #1343

Author: aaronroberson

Diff for: src/uiSelectMultipleDirective.js

@@ -107,8 +107,8 @@ uis.directive('uiSelectMultiple', ['uiSelectMinErr','$timeout', function(uiSelec
             if($select.parserResult.trackByExp){
                 var propsItemNameMatches = /(\w*)\./.exec($select.parserResult.trackByExp);
                 var matches = /\.([^\s]+)/.exec($select.parserResult.trackByExp);
-                if(propsItemNameMatches.length > 0 && propsItemNameMatches[1] == $select.parserResult.itemName){
-                  if(matches.length>0 && result[matches[1]] == value[matches[1]]){
+                if(propsItemNameMatches && propsItemNameMatches.length > 0 && propsItemNameMatches[1] == $select.parserResult.itemName){
+                  if(matches && matches.length>0 && result[matches[1]] == value[matches[1]]){
                       resultMultiple.unshift(list[p]);
                       return true;
                   }