Combat AI: Don't attempt to cast spells when impossible to succeed (Fixes #2059)

apps/openmw/mwmechanics/aicombataction.cpp

@@ -9,6 +9,7 @@
 #include "../mwworld/actionequip.hpp"
 
 #include "../mwmechanics/npcstats.hpp"
+#include "../mwmechanics/spellcasting.hpp"
 
 #include <components/esm/loadench.hpp>
 #include <components/esm/loadmgef.hpp>
@@ -166,6 +167,9 @@ namespace MWMechanics
     {
         const CreatureStats& stats = actor.getClass().getCreatureStats(actor);
 
+        if (MWMechanics::getSpellSuccessChance(spell, actor) == 0)
+            return 0.f;
+
         if (spell->mData.mType != ESM::Spell::ST_Spell)
             return 0.f;