Error in com_categories in multilang and postgres

## Executive Summary
The group by clause when in multilingual mode in postgres breaks the query

## Testing instructions
In mysql check the categories list view continues to work as expected.

In postgres you'll see the popular and latest news modules will give php errors and sql errors. Also the articles list view itself will give SQL errors and not show. Apply the patch and the list view should work as expected.

N.B. In order to get multilang working on postgres you'll need to either install the languages in the backend or  apply these two patches (https://github.com/joomla/joomla-cms/pull/4969 and https://github.com/joomla/joomla-cms/pull/4942) to use the multilang installer during Joomla installation