Gamepad and joystick dead zone fix

Fix for gamepad and joystick dead zone calculation so that the
calculated value will always fall within the 0..1 range.  In reference
to https://github.com/GarageGames/Torque3D/issues/468
Merge pull request #483 from DavidWyand-GG/JoystickDeadZoneFix

Gamepad and joystick dead zone fix