Fix crashes on exit in the LightManager (bug #6044)

components/sceneutil/lightmanager.cpp

@@ -439,7 +439,11 @@ namespace SceneUtil
 
         void apply(osg::State &state) const override
         {
-            auto* lightUniform = mLightManager->getStateSet()->getUniform("LightBuffer");
+            osg::StateSet* stateSet = mLightManager->getStateSet();
+            if (!stateSet)
+                return;
+
+            auto* lightUniform = stateSet->getUniform("LightBuffer");
             for (size_t i = 0; i < mLights.size(); ++i)
             {
                 auto light = mLights[i];
@@ -832,6 +836,11 @@ namespace SceneUtil
         return "";
     }
 
+    LightManager::~LightManager()
+    {
+        getOrCreateStateSet()->removeAttribute(osg::StateAttribute::LIGHT);
+    }
+
     LightManager::LightManager(bool ffp)
         : mStartLight(0)
         , mLightingMask(~0u)

components/sceneutil/lightmanager.hpp

@@ -137,6 +137,8 @@ namespace SceneUtil
 
         LightManager(const LightManager& copy, const osg::CopyOp& copyop);
 
+        ~LightManager();
+
         /// @param mask This mask is compared with the current Camera's cull mask to determine if lighting is desired.
         /// By default, it's ~0u i.e. always on.
         /// If you have some views that do not require lighting, then set the Camera's cull mask to not include