Desktop Support: null error when getting tracker

[pietru2004]

addons\godot-xr-tools\objects\grab_points\grab_point_hand.gd

Whenever any code tries to use var tracker := XRServer.get_tracker(controller.tracker) as XRPositionalTracker when in desktop support mode it returns null which causes errors.
There should be some default behaviour for desktop support or when tracker is null

Example code to make items equipped into hands when player is in desktop mode.

var _pickup_right_node : XRToolsFunctionPickup
func select_item(target: Node3D):
	if !is_instance_valid(target):
		return
	var dropped_item=_pickup_right_node.picked_up_object
	_pickup_right_node._pick_up_object(target)
	right_held=target
	handle_dropped_item(dropped_item)