Avoid copying osg::ref_ptr when adding or removing item from work queue

Copy constructor does refcounting, and move constructor doesn't.

apps/openmw/mwrender/renderingmanager.cpp

@@ -492,7 +492,7 @@ namespace MWRender
 
         workItem->mTextures.emplace_back("textures/_land_default.dds");
 
-        mWorkQueue->addWorkItem(workItem);
+        mWorkQueue->addWorkItem(std::move(workItem));
     }
 
     double RenderingManager::getReferenceTime() const

components/sceneutil/workqueue.cpp

@@ -74,9 +74,9 @@ void WorkQueue::addWorkItem(osg::ref_ptr<WorkItem> item, bool front)
 
     std::unique_lock<std::mutex> lock(mMutex);
     if (front)
-        mQueue.push_front(item);
+        mQueue.push_front(std::move(item));
     else
-        mQueue.push_back(item);
+        mQueue.push_back(std::move(item));
     mCondition.notify_one();
 }
 
@@ -89,7 +89,7 @@ osg::ref_ptr<WorkItem> WorkQueue::removeWorkItem()
     }
     if (!mQueue.empty())
     {
-        osg::ref_ptr<WorkItem> item = mQueue.front();
+        osg::ref_ptr<WorkItem> item = std::move(mQueue.front());
         mQueue.pop_front();
         return item;
     }