Renderer: Improve null renderer performance (#646)

* Renderer: Improve null renderer performance

* Update frontend_sdl.cpp

include/renderer_null/renderer_null.hpp

@@ -17,6 +17,10 @@ class RendererNull final : public Renderer {
 	void screenshot(const std::string& name) override;
 	void deinitGraphicsContext() override;
 
+	// Tell the GPU core that we'll handle vertex fetch & shader execution in the renderer in order to speed up execution.
+	// Of course, we don't do this and geometry is never actually processed, since this is the null renderer.
+	virtual bool prepareForDraw(ShaderUnit& shaderUnit, PICA::DrawAcceleration* accel) override { return true; };
+
 #ifdef PANDA3DS_FRONTEND_QT
 	virtual void initGraphicsContext([[maybe_unused]] GL::Context* context) override {}
 #endif