fix(typeahead): do not execute unnecessary $digest

- If in a $digest, do not execute `scope.$digest`

Fixes #2652
Closes #3791

Author: wesleycho

src/typeahead/typeahead.js

@@ -29,8 +29,8 @@ angular.module('ui.bootstrap.typeahead', ['ui.bootstrap.position', 'ui.bootstrap
   };
 }])
 
-  .directive('typeahead', ['$compile', '$parse', '$q', '$timeout', '$document', '$position', 'typeaheadParser',
-    function ($compile, $parse, $q, $timeout, $document, $position, typeaheadParser) {
+  .directive('typeahead', ['$compile', '$parse', '$q', '$timeout', '$document', '$rootScope', '$position', 'typeaheadParser',
+    function ($compile, $parse, $q, $timeout, $document, $rootScope, $position, typeaheadParser) {
 
   var HOT_KEYS = [9, 13, 27, 38, 40];
 
@@ -318,7 +318,9 @@ angular.module('ui.bootstrap.typeahead', ['ui.bootstrap.position', 'ui.bootstrap
       var dismissClickHandler = function (evt) {
         if (element[0] !== evt.target) {
           resetMatches();
-          scope.$digest();
+          if (!$rootScope.$$phase) {
+            scope.$digest();
+          }
         }
       };