Do not lose existing callbacks for sky node

apps/openmw/mwrender/precipitationocclusion.cpp

@@ -147,7 +147,8 @@ namespace MWRender
 
     void PrecipitationOccluder::enable()
     {
-        mSkyNode->setCullCallback(new PrecipitationOcclusionUpdater(mDepthTexture));
+        mSkyCullCallback = new PrecipitationOcclusionUpdater(mDepthTexture);
+        mSkyNode->addCullCallback(mSkyCullCallback);
         mCamera->setCullCallback(new DepthCameraUpdater);
 
         mRootNode->removeChild(mCamera);
@@ -156,8 +157,9 @@ namespace MWRender
 
     void PrecipitationOccluder::disable()
     {
-        mSkyNode->setCullCallback(nullptr);
+        mSkyNode->removeCullCallback(mSkyCullCallback);
         mCamera->setCullCallback(nullptr);
+        mSkyCullCallback = nullptr;
 
         mRootNode->removeChild(mCamera);
     }

apps/openmw/mwrender/precipitationocclusion.hpp

@@ -23,6 +23,7 @@ namespace MWRender
         osg::Group* mSkyNode;
         osg::Group* mSceneNode;
         osg::Group* mRootNode;
+        osg::ref_ptr<osg::Callback> mSkyCullCallback;
         osg::ref_ptr<osg::Camera> mCamera;
         osg::ref_ptr<osg::Camera> mSceneCamera;
         osg::ref_ptr<osg::Texture2D> mDepthTexture;