fixed: TSDLWindow::GetWindowHandle always returned null

SDL_config.h wasn't included, so the ifdef driver checks in bmx_sdl_video_GetWindowHandle were all skipped, resulting in a NULL return

sdlvideo.mod/glue.c

@@ -20,6 +20,7 @@
     3. This notice may not be removed or altered from any source
     distribution.
 */
+#include "SDL_config.h"
 #include "SDL_video.h"
 #include "SDL_syswm.h"