[ticket/12964] Correct use of undefined $row variable.

PHPBB3-12964
Merge pull request #2866 from bantu/ticket/12964

[ticket/12964] Correct use of undefined $row variable.
[ticket/12944] Add core.login_forum_box core event

Add core.login_forum_box core event to allow extensions
performing additional actions on forum login.

PHPBB3-12944
Merge pull request #2863 from rxu/ticket/12944

[ticket/12944] Add core.login_forum_box core event