[ticket/12929] core.ucp_pm_compose_compose_pm_basic_info_query_before

Adding the core.ucp_pm_compose_compose_pm_basic_info_query_before
event to ucp backend.

https://tracker.phpbb.com/browse/PHPBB3-12929

PHPBB3-12929
there is no topic_id here?
I guess you mean `msg_id`