fix(datepicker popup): convert non-date values to date before parsing

Fixes angular-ui#5871

Author: mebibou

src/datepickerPopup/popup.js

@@ -133,12 +133,12 @@ function($scope, $element, $attrs, $compile, $log, $parse, $window, $document, $
           return value;
         }
 
-        $scope.date = dateParser.fromTimezone(value, timezone);
-
-        if (angular.isNumber($scope.date)) {
-          $scope.date = new Date($scope.date);
+        if (angular.isNumber(value)) {
+          value = new Date(value);
         }
 
+        $scope.date = dateParser.fromTimezone(value, timezone);
+
         return dateParser.filter($scope.date, dateFormat);
       });
     } else {