[ticket/12880] core.mcp_queue_!is_topics_query_before

Adding core.mcp_queue_!is_topics_query_before

https://tracker.phpbb.com/browse/PHPBB3-12880

PHPBB3-12880
I don't know. I may never be false and it may only ever be 0. I just wrote like that in order to be on the safe side.
if: `topic_id = 0`
`topic_id != false` is false
`topic_id != 0` is false
`topic_id == false` is true

I'll mention 0, then. By reading the code, I don't think that it is ever the boolean false.