On windows, with current (2.0.8) SDL version, if two joysticks are plugged SDL initially enumerates them as:

[SDL2] Joystick number 0 -- "Saitek X45"
  --> Buttons: 26
  -->    Axis: 6
  -->    Hats: 1
  -->   Balls: 0
  -->    GUID: "03000000a30600003c05000000000000"
[SDL2] Joystick number 1 -- "Generic   USB  Joystick  "
  --> Buttons: 12
  -->    Axis: 5
  -->    Hats: 1
  -->   Balls: 0
  -->    GUID: "03000000790000000600000000000000"

But immediately the events generated by Joystick 0 (Saitek X45) have the event `which` attribute set to 1, and the events generated by the joystick 0 (Generic) have the `which`attribute set to 1.

More worrying, if I disconnect joystick 1 (Generic) and whenever an event from Joystick 0 (Saitek) is received I call `SDL_JoystickGetDeviceGUID` with the events' `which` value, it will still be 1 and the returned GUID will be all-zero.

How to reproduce:
- Enumerate and open all joystick devices (SDL_JoystickOpen).
- register an event callback (SDL_AddEventWatch).
- Whenever a joystick event is received, call SDL_JoystickGetDeviceGUID with `which`as an argument.

At this point, printing the event `which`argument should be swapped around between joystick 1 and 0. The device enumerated as '0' will have '1' on the `which` attribute and the other way around.

- Disconnect device 1
- Move device 0
- the returned GUID will be all-zero and the event `which` value should still be swapped. Somehow I am receiving events from a device that does not exist/have GUID.