sdl: Fix termination in -no-shutdown mode

Just like the monitor does, we need to clear no_shutdown before calling
qemu_system_shutdown_request on quit requests. Otherwise, QEMU just
stops the VM.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

ui/sdl.c

@@ -672,8 +672,10 @@ static void sdl_refresh(DisplayState *ds)
                 sdl_process_key(&ev->key);
             break;
         case SDL_QUIT:
-            if (!no_quit)
+            if (!no_quit) {
+                no_shutdown = 0;
                 qemu_system_shutdown_request();
+            }
             break;
         case SDL_MOUSEMOTION:
             if (gui_grab || kbd_mouse_is_absolute() ||