Fix incorrect icon image path for DatePicker button (#40559, #39111).

Patch by Katsuya HIDAKA (hidakatsuya).

git-svn-id: https://svn.redmine.org/redmine/trunk@22784 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/helpers/application_helper.rb

@@ -1644,7 +1644,7 @@ module ApplicationHelper
           javascript_tag(
             "var datepickerOptions={dateFormat: 'yy-mm-dd', firstDay: #{start_of_week}, " \
               "showOn: 'button', buttonImageOnly: true, buttonImage: '" +
-            path_to_image('/images/calendar.png') +
+            asset_path('calendar.png') +
               "', showButtonPanel: true, showWeek: true, showOtherMonths: true, " \
               "selectOtherMonths: true, changeMonth: true, changeYear: true, " \
               "beforeShow: beforeShowDatePicker};"