Fix reloading scene debug issue (#310)

* 🐛 unregister behaviour tree from debugging when removed from scene

* Fix tabs being spaces, I hope

* Check if active tree is valid before trying to do things with it

addons/beehave/debug/global_debugger.gd

@@ -13,7 +13,7 @@ func _on_debug_message(message: String, data: Array) -> bool:
 		_set_active_tree(data[0])
 		return true
 	if message == "visibility_changed":
-		if _active_tree:
+		if _active_tree && is_instance_valid(_active_tree):
 			_active_tree._can_send_message = data[0]
 		return true
 	return false
@@ -24,7 +24,7 @@ func _set_active_tree(tree_id: int) -> void:
 	if not tree:
 		return
 
-	if _active_tree:
+	if _active_tree && is_instance_valid(_active_tree):
 		_active_tree._can_send_message = false
 	_active_tree = tree
 	_active_tree._can_send_message = true

addons/beehave/nodes/beehave_tree.gd

@@ -149,10 +149,15 @@ func _on_scene_tree_node_added_removed(node: Node, is_added: bool) -> void:
 
 	if node is BeehaveNode and is_ancestor_of(node):
 		var sgnal := node.ready if is_added else node.tree_exited
-		sgnal.connect(
-			func() -> void: BeehaveDebuggerMessages.register_tree(_get_debugger_data(self)),
-			CONNECT_ONE_SHOT
-		)
+		if is_added:
+			sgnal.connect(
+				func() -> void: BeehaveDebuggerMessages.register_tree(_get_debugger_data(self)),
+				CONNECT_ONE_SHOT
+			)
+		else:
+			sgnal.connect(
+				func() -> void: BeehaveDebuggerMessages.unregister_tree(get_instance_id())
+			)
 
 
 func _physics_process(_delta: float) -> void: