Error in com_newsfeeds 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 newsfeeds list view continues to work as expected in the backend.

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