Fetch all catalog tables at once to avoid conflicts with buffered query results

[bezin]

When upgrading a Contao project from 4.13 to 5.3. I ran in to the folllwing error message:

General error: 2014 Cannot execute queries while other unbuffered queries are active. Consider using PDOStatement::fetchAll(). …

This was caused by running queries inside the while loop. This PR fixes this by loading all catalog tables at once.