fix(ControllerEvents): ensure touchpad axis reset to zero on untouch

The touchpad axis needs to be reset to zero when the touchpad is
untouched otherwise it will remember the previous touchpad axis state.

Assets/VRTK/Scripts/Interactions/VRTK_ControllerEvents.cs

@@ -1174,6 +1174,7 @@ protected virtual void Update()
             if (!touchpadTouched || Vector2ShallowEquals(touchpadAxis, currentTouchpadAxis))
             {
                 touchpadAxisChanged = false;
+                touchpadAxis = Vector2.zero;
             }
             else
             {