[AD] Timer bug

[Thomas Fjellstrom <tfjellstrom@xxxxxxxxxx>]

Just playing with allegro a bit, and creating a timer with 
al_create_timer(1/60); causes al_destroy_timer and al_stop_timer to lock up on 
the timer mutex.

I think it should either fail if the timeout is invalid, or default it to the 
smallest possible value that won't kill things if it is even possible to 
detect that.

-- 
Thomas Fjellstrom
tfjellstrom@xxxxxxxxxx