Use const references when possible in for loops

No need for useless copies.

apps/openmw/mwgui/dialogue.cpp

@@ -306,7 +306,7 @@ namespace MWGui
         deleteLater();
         for (Link* link : mLinks)
             delete link;
-        for (auto link : mTopicLinks)
+        for (const auto& link : mTopicLinks)
             delete link.second;
         for (auto history : mHistoryContents)
             delete history;

apps/openmw/mwmechanics/spelllist.cpp

@@ -70,7 +70,7 @@ namespace MWMechanics
         auto& id = spell->mId;
         bool changed = withBaseRecord([&] (auto& spells)
         {
-            for(auto it : spells)
+            for(const auto& it : spells)
             {
                 if(Misc::StringUtils::ciEqual(id, it))
                     return false;

apps/openmw/mwrender/objectpaging.cpp

@@ -743,7 +743,7 @@ namespace MWRender
         ccf.mCell = cell;
         mCache->call(ccf);
         if (ccf.mToClear.empty()) return false;
-        for (auto chunk : ccf.mToClear)
+        for (const auto& chunk : ccf.mToClear)
             mCache->removeFromObjectCache(chunk);
         return true;
     }
@@ -765,7 +765,7 @@ namespace MWRender
         ccf.mActiveGridOnly = true;
         mCache->call(ccf);
         if (ccf.mToClear.empty()) return false;
-        for (auto chunk : ccf.mToClear)
+        for (const auto& chunk : ccf.mToClear)
             mCache->removeFromObjectCache(chunk);
         return true;
     }

apps/openmw/mwworld/esmstore.cpp

@@ -63,7 +63,7 @@ namespace
         // We will replace invalid entries by fixed ones
         std::vector<ESM::NPC> npcsToReplace;
 
-        for (auto npcIter : npcs)
+        for (const auto& npcIter : npcs)
         {
             ESM::NPC npc = npcIter.second;
             bool changed = false;