Artf4800: Fixes HALGetJoystick*** Segfault
Artf4800: Fixes HALGetJoystick*** Segfault

The HALGetJoystick*** methods were not initializing the descriptor
variable properly. This was causing a SegFault if joysticks were moved
around while one of these methods were running.

Change-Id: If804c7ea724b10381765068e4d6fad75fad69ecb

PeterMitrano/allwpilib,RAR1741/wpilib,JLLeitschuh/allwpilib,JLLeitschuh/allwpilib,333fred/allwpilib,robotdotnet/allwpilib,PeterMitrano/allwpilib,333fred/allwpilib,333fred/allwpilib,JLLeitschuh/allwpilib,PeterMitrano/allwpilib,PatrickPenguinTurtle/allwpilib,robotdotnet/allwpilib,PatrickPenguinTurtle/allwpilib,RAR1741/wpilib,robotdotnet/allwpilib,JLLeitschuh/allwpilib,RAR1741/wpilib,robotdotnet/allwpilib,PeterMitrano/allwpilib,PeterMitrano/allwpilib,JLLeitschuh/allwpilib,robotdotnet/allwpilib,PeterMitrano/allwpilib,RAR1741/wpilib,333fred/allwpilib,333fred/allwpilib,333fred/allwpilib,JLLeitschuh/allwpilib,PeterMitrano/allwpilib,PatrickPenguinTurtle/allwpilib,RAR1741/wpilib,robotdotnet/allwpilib,RAR1741/wpilib,PatrickPenguinTurtle/allwpilib,PatrickPenguinTurtle/allwpilib,PatrickPenguinTurtle/allwpilib,JLLeitschuh/allwpilib,PatrickPenguinTurtle/allwpilib,RAR1741/wpilib