GlobalShortcut_win: check for xboxinput != NULL before use.
GlobalShortcut_win: check for xboxinput != NULL before use.

With the ability to change the enabled state for XboxInput at runtime,
we now need these additional checks to avoid crashes.

Lartza/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble,Lartza/mumble