Don't applyInstantEffect when magnitude is zero

apps/openmw/mwmechanics/actors.cpp

@@ -494,10 +494,13 @@ namespace MWMechanics
                 effectTick(creatureStats, ptr, it->first, it->second.getMagnitude() * duration);
 
                 // instant effects are already applied on spell impact in spellcasting.cpp, but may also come from permanent abilities
+                if (it->second.getMagnitude() > 0)
+                {
                     CastSpell cast(ptr, ptr);
                     cast.applyInstantEffect(ptr, ptr, it->first, it->second.getMagnitude());
                 }
             }
+        }
 
         // attributes
         for(int i = 0;i < ESM::Attribute::Length;++i)