fix(datepicker): commit safe apply on destruction

- Ensure we are not in a $digest before executing an $apply on scope destruction to avoid potential error

Closes #4079
Fixes #4076

Author: wesleycho

src/datepicker/datepicker.js

@@ -474,8 +474,8 @@ angular.module('ui.bootstrap.datepicker', ['ui.bootstrap.dateparser', 'ui.bootst
   showButtonBar: true
 })
 
-.directive('datepickerPopup', ['$compile', '$parse', '$document', '$position', 'dateFilter', 'dateParser', 'datepickerPopupConfig', '$timeout',
-function ($compile, $parse, $document, $position, dateFilter, dateParser, datepickerPopupConfig, $timeout) {
+.directive('datepickerPopup', ['$compile', '$parse', '$document', '$rootScope', '$position', 'dateFilter', 'dateParser', 'datepickerPopupConfig', '$timeout',
+function ($compile, $parse, $document, $rootScope, $position, dateFilter, dateParser, datepickerPopupConfig, $timeout) {
   return {
     restrict: 'EA',
     require: 'ngModel',
@@ -749,9 +749,11 @@ function ($compile, $parse, $document, $position, dateFilter, dateParser, datepi
 
       scope.$on('$destroy', function() {
         if (scope.isOpen === true) {
-          scope.$apply(function() {
-            scope.isOpen = false;
-          });
+          if (!$rootScope.$$phase) {
+            scope.$apply(function() {
+              scope.isOpen = false;
+            });
+          }
         }
 
         $popup.remove();