ui/sdl2: Grab Alt+F4 also under Windows

SDL doesn't grab Alt+F4 under Windows by default. Pressing Alt+F4 thus closes
the VM immediately without confirmation, possibly leading to data loss. Fix
this by always grabbing Alt+F4 on Windows hosts, too.

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: Volker Rümelin <vr_qemu@t-online.de>
Message-Id: <20230417192139.43263-3-shentey@gmail.com>
(cherry picked from commit 083db9d)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

ui/sdl2.c

@@ -859,6 +859,7 @@ static void sdl2_display_init(DisplayState *ds, DisplayOptions *o)
 #ifdef SDL_HINT_ALLOW_ALT_TAB_WHILE_GRABBED
     SDL_SetHint(SDL_HINT_ALLOW_ALT_TAB_WHILE_GRABBED, "0");
 #endif
+    SDL_SetHint(SDL_HINT_WINDOWS_NO_CLOSE_ON_ALT_F4, "1");
     memset(&info, 0, sizeof(info));
     SDL_VERSION(&info.version);