ApiThreadAction: Make sure a Title is set

This is a total hack, but I don't want to fix this extension,
and it fixes MassMessage LQT support.

This was probably caused by someone removing an instance of
$wgTitle from somewhere.

Bug: 71081
Change-Id: Ieafbcbdd03cf038a4834f71537d8ddd84afea6cd
(cherry picked from commit e70f3e0f9b603f65a2fe72dbb0d6bc211d56cf46)