#5893: Clear entities and lights while modules are still alive.

This is most likely due to unclean removal of attached light entities when their host entities are removed from the scene, so this is a defensive step.

radiantcore/rendersystem/OpenGLRenderSystem.cpp

@@ -578,6 +578,9 @@ void OpenGLRenderSystem::initialiseModule(const IApplicationContext& ctx)
 
 void OpenGLRenderSystem::shutdownModule()
 {
+    _entities.clear();
+    _lights.clear();
+
     _textRenderers.clear();
 
     _sharedContextCreated.disconnect();