Fix alchemy allowing same item ID in different slots (Fixes #1407)

apps/openmw/mwmechanics/alchemy.cpp

@@ -395,7 +395,8 @@ int MWMechanics::Alchemy::addIngredient (const MWWorld::Ptr& ingredient)
         return -1;
 
     for (TIngredientsIterator iter (mIngredients.begin()); iter!=mIngredients.end(); ++iter)
-        if (!iter->isEmpty() && ingredient.get<ESM::Ingredient>()==iter->get<ESM::Ingredient>())
+        if (!iter->isEmpty() && Misc::StringUtils::ciEqual(ingredient.getClass().getId(ingredient),
+                                                           iter->getClass().getId(*iter)))
             return -1;
 
     mIngredients[slot] = ingredient;