Fix invalid Skeleton3D bone pose updates

The issue would cause log spams when trying to update the bone pose position or rotation with an invalid bone index.

(cherry picked from commit 039722a341)

scene/3d/xr_hand_modifier_3d.cpp

@@ -207,6 +207,11 @@ void XRHandModifier3D::_process_modification() {
 
 		// Apply previous relative transforms if they are stored.
 		for (int joint = 0; joint < XRHandTracker::HAND_JOINT_MAX; joint++) {
+			const int bone = joints[joint].bone;
+			if (bone == -1) {
+				continue;
+			}
+
 			if (bone_update == BONE_UPDATE_FULL) {
 				skeleton->set_bone_pose_position(joints[joint].bone, previous_relative_transforms[joint].origin);
 			}