Codechange: [SDL2] Split driver in base-part and default backend

src/video/sdl2_opengl_v.h

@@ -10,7 +10,7 @@
 #include "sdl2_v.h"
 
 /** The OpenGL video driver for windows. */
-class VideoDriver_SDL_OpenGL : public VideoDriver_SDL {
+class VideoDriver_SDL_OpenGL : public VideoDriver_SDL_Base {
 public:
 	VideoDriver_SDL_OpenGL() : gl_context(nullptr), anim_buffer(nullptr) {}
 
@@ -36,6 +36,8 @@ protected:
 	void Paint() override;
 	bool CreateMainWindow(uint w, uint h, uint flags) override;
 
+	void PaintThread() override {}
+
 private:
 	void  *gl_context;  ///< OpenGL context.
 	uint8 *anim_buffer; ///< Animation buffer from OpenGL back-end.