Default SDL_HINT_JOYSTICK_GAMEINPUT to SDL_FALSE

This was causing crashes in IGameInput_RegisterSystemButtonCallback(), presumably on older systems with runtimes using a different function signature. We'll just disable it for now until the GameInput runtime has stabilized and we can tell when it's safe to use.

src/joystick/gdk/SDL_gameinputjoystick.c

@@ -234,7 +234,7 @@ static int GAMEINPUT_JoystickInit(void)
 {
     HRESULT hR;
 
-    if (!SDL_GetHintBoolean(SDL_HINT_JOYSTICK_GAMEINPUT, true)) {
+    if (!SDL_GetHintBoolean(SDL_HINT_JOYSTICK_GAMEINPUT, false)) {
         return 0;
     }