fix uiselectmultiple initialization

Author: stefanopoli

src/uiselectmultiple.html

@@ -1,6 +1,6 @@
 
 <div class="form-group" ng-class="{'has-error': hasError(), 'has-success': hasSuccess(), 'has-feedback': form.feedback !== false}"
-        ng-controller="dynamicSelectController" ng-init="uiMultiSelectInitInternalModel($$value$$)">
+        ng-controller="dynamicSelectController" ng-init="$$value$$=$$value$$||[];uiMultiSelectInitInternalModel($$value$$)">
   <label class="control-label" ng-show="showTitle()">{{form.title}}</label>
   <div class="form-group">
     <ui-select multiple sortable-options="{{form.sortableOptions}}" ng-model="internalModel" theme="bootstrap"