[ticket/13310] Always use sql_build_query in acp_email.php

PHPBB3-13310
[ticket/13310] Add event core.acp_email_modify_sql

PHPBB3-13310
Merge pull request #3123 from Elsensee/ticket/13310

[ticket/13310] Add event core.acp_email_modify_sql
Merge branch 'develop-ascraeus' into develop