AI sometimes spams defensive spells

Try to attack anyone on "Balmora, Guild of Mages".

You may notice that Masalinie Merian sometimes casts "reflect" repeatedly, even if this spell was already casted a couple of seconds ago, Ajira spams spell absorbtion.

I also tried to add "bound longbow" spell to Missun Akin. He casts this spell three times in row before starts to use a summoned bow.

I think there is a bug in aicombataction.cpp - rateEffect() does not check if actor already has the same effect.

(RM-3855 from redmine: created on 2017-05-02 by Andrei Kortunov, , relates #3406 (closed))

Attachments: aicombataction-cpp-prepareNextAction.txt aicombataction.cpp