[ticket/12317] Do not repeat SQL query in notification_submit_post_base.

PHPBB3-12317
[ticket/12317] Fix notification tests for DBMSes returning integers as int.

PHPBB3-12317
[ticket/12317] Cast string to int to refix DBMSes not using int for integers.

PHPBB3-12317
Merge pull request #2194 from bantu/ticket/12317

[ticket/12317] Fix notification tests for DBMS drivers using int for integers ;-)