Correct Error $compile:nonassign

Author: l-lin

dist/angular-datatables.js

@@ -129,7 +129,7 @@ function dataTable($q, $http, DTRendererFactory, DTRendererService, DTPropertyUt
         function _setDTInstance(dtInstance) {
             if (angular.isFunction($scope.dtInstance)) {
                 $scope.dtInstance(dtInstance);
-            } else {
+            } else if (angular.isDefined($scope.dtInstance)) {
                 $scope.dtInstance = dtInstance;
             }
         }