Added support for simulated vsync in the renderer

This kicks in if the platform doesn't support vsync directly, or if the present fails for some reason (e.g. minimized on some platforms)

Fixes https://github.com/libsdl-org/SDL/issues/5134

src/render/software/SDL_render_sw.c

@@ -983,14 +983,15 @@ SW_RenderReadPixels(SDL_Renderer * renderer, const SDL_Rect * rect,
                              format, pixels, pitch);
 }
 
-static void
+static int
 SW_RenderPresent(SDL_Renderer * renderer)
 {
     SDL_Window *window = renderer->window;
 
-    if (window) {
-        SDL_UpdateWindowSurface(window);
+    if (!window) {
+        return -1;
     }
+    return SDL_UpdateWindowSurface(window);
 }
 
 static void