XInputCheck: add documentation for XInputCheck_IsGuidProductXInputDevice.
XInputCheck: add documentation for XInputCheck_IsGuidProductXInputDevice.

Lartza/mumble,unascribed/mumble,Lartza/mumble,Lartza/mumble,SuperNascher/mumble,Lartza/mumble,SuperNascher/mumble,unascribed/mumble,unascribed/mumble,Lartza/mumble,Lartza/mumble,SuperNascher/mumble,LuAPi/mumble,SuperNascher/mumble,SuperNascher/mumble,SuperNascher/mumble,Lartza/mumble,LuAPi/mumble,unascribed/mumble,SuperNascher/mumble,Lartza/mumble,LuAPi/mumble,LuAPi/mumble,LuAPi/mumble,LuAPi/mumble,SuperNascher/mumble,unascribed/mumble,LuAPi/mumble,unascribed/mumble,SuperNascher/mumble,unascribed/mumble,LuAPi/mumble,unascribed/mumble,LuAPi/mumble