Accept that it's too much work to defer light manager creation in the CS and instead use something akin to the old approach

components/sceneutil/glextensions.cpp

@@ -33,6 +33,11 @@ namespace SceneUtil
         GLExtensionsObserver GLExtensionsObserver::sInstance{};
     }
 
+    bool glExtensionsReady()
+    {
+        return !sGLExtensions.empty();
+    }
+
     osg::GLExtensions& getGLExtensions()
     {
         if (sGLExtensions.empty())

components/sceneutil/glextensions.hpp

@@ -6,6 +6,7 @@
 
 namespace SceneUtil
 {
+    bool glExtensionsReady();
     osg::GLExtensions& getGLExtensions();
 
     class GetGLExtensionsOperation : public osg::GraphicsOperation

components/sceneutil/lightmanager.cpp

@@ -825,9 +825,9 @@ namespace SceneUtil
         , mPointLightFadeEnd(0.f)
         , mPointLightFadeStart(0.f)
     {
-        osg::GLExtensions& exts = SceneUtil::getGLExtensions();
-        bool supportsUBO = exts.isUniformBufferObjectSupported;
-        bool supportsGPU4 = exts.isGpuShader4Supported;
+        osg::GLExtensions* exts = SceneUtil::glExtensionsReady() ? &SceneUtil::getGLExtensions() : nullptr;
+        bool supportsUBO = exts && exts->isUniformBufferObjectSupported;
+        bool supportsGPU4 = exts && exts->isGpuShader4Supported;
 
         mSupported[static_cast<int>(LightingMethod::FFP)] = true;
         mSupported[static_cast<int>(LightingMethod::PerObjectUniform)] = true;