Error in com_menus in multilang and postgres

## Executive Summary
The group by clause when in multilingual mode in postgres breaks the query

## Testing instructions
In mysql and postgres check the list of menu items continues to work as expected in the backend. Check the list displays and if you want you can test filtering.

N.B. In order to get multilang working on postgres you'll need to either install the languages in the backend or  apply this patch (https://github.com/joomla/joomla-cms/pull/4969) to use the multilang installer during Joomla installation