Cache absent land object

This allows to save on lookup in store.

apps/openmw/mwrender/landmanager.cpp

@@ -19,9 +19,8 @@ namespace MWRender
 
     osg::ref_ptr<ESMTerrain::LandObject> LandManager::getLand(ESM::ExteriorCellLocation cellIndex)
     {
-        const osg::ref_ptr<osg::Object> obj = mCache->getRefFromObjectCache(cellIndex);
-        if (obj != nullptr)
-            return static_cast<ESMTerrain::LandObject*>(obj.get());
+        if (const std::optional<osg::ref_ptr<osg::Object>> obj = mCache->getRefFromObjectCacheOrNone(cellIndex))
+            return static_cast<ESMTerrain::LandObject*>(obj->get());
 
         const MWBase::World& world = *MWBase::Environment::get().getWorld();
         osg::ref_ptr<ESMTerrain::LandObject> landObj = nullptr;
@@ -29,16 +28,14 @@ namespace MWRender
         if (ESM::isEsm4Ext(cellIndex.mWorldspace))
         {
             const ESM4::Land* land = world.getStore().get<ESM4::Land>().search(cellIndex);
-            if (land == nullptr)
-                return nullptr;
-            landObj = new ESMTerrain::LandObject(*land, mLoadFlags);
+            if (land != nullptr)
+                landObj = new ESMTerrain::LandObject(*land, mLoadFlags);
         }
         else
         {
             const ESM::Land* land = world.getStore().get<ESM::Land>().search(cellIndex.mX, cellIndex.mY);
-            if (land == nullptr)
-                return nullptr;
-            landObj = new ESMTerrain::LandObject(*land, mLoadFlags);
+            if (land != nullptr)
+                landObj = new ESMTerrain::LandObject(*land, mLoadFlags);
         }
 
         mCache->addEntryToObjectCache(cellIndex, landObj.get());

components/resource/objectcache.hpp

@@ -26,6 +26,7 @@
 
 #include <map>
 #include <mutex>
+#include <optional>
 #include <string>
 
 namespace osg
@@ -82,7 +83,8 @@ namespace Resource
                 {
                     if (oitr->second.second <= expiryTime)
                     {
-                        objectsToRemove.push_back(oitr->second.first);
+                        if (oitr->second.first != nullptr)
+                            objectsToRemove.push_back(oitr->second.first);
                         _objectCache.erase(oitr++);
                     }
                     else
@@ -127,6 +129,15 @@ namespace Resource
                 return nullptr;
         }
 
+        std::optional<osg::ref_ptr<osg::Object>> getRefFromObjectCacheOrNone(const KeyType& key)
+        {
+            const std::lock_guard<std::mutex> lock(_objectCacheMutex);
+            const auto it = _objectCache.find(key);
+            if (it == _objectCache.end())
+                return std::nullopt;
+            return it->second.first;
+        }
+
         /** Check if an object is in the cache, and if it is, update its usage time stamp. */
         bool checkInObjectCache(const KeyType& key, double timeStamp)
         {