Fix chained custom field filter doesn't work for User fields (#36940).

Patch by Thomas Löber.



git-svn-id: https://svn.redmine.org/redmine/trunk@21686 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/query.rb

@@ -1176,7 +1176,7 @@ class Query < ActiveRecord::Base
     end
 
     filter = available_filters[field]
-    target_class = filter[:through].format.target_class
+    target_class = filter[:through].format.target_class.base_class
 
     "#{queried_table_name}.id #{not_in} IN (" +
       "SELECT customized_id FROM #{CustomValue.table_name}" +