Create a fake desktop mode for windowed mode apps

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%401956

src/video/dummy/SDL_nullvideo.c

@@ -109,7 +109,12 @@ DUMMY_VideoInit(_THIS)
 {
     SDL_DisplayMode mode;
 
-    SDL_AddBasicVideoDisplay(NULL);
+    /* Use a fake 32-bpp desktop mode */
+    mode.format = SDL_PixelFormat_RGB888;
+    mode.w = 1024;
+    mode.h = 768;
+    mode.refresh_rate = 0;
+    SDL_AddBasicVideoDisplay(&mode);
     SDL_AddRenderDriver(0, &SDL_DUMMY_RenderDriver);
 
     SDL_zero(mode);