### Godot version

master ([06ccbfe](https://github.com/godotengine/godot/commit/06ccbfe8eec6e840db3df2360dc2804386f940b8))

### System information

PopOS 22.04

### Issue description

Sometimes the doc page is broken when the engine is closed and then restarted.
Closing the doc and opening it again fixes it.

![2023-05-27_22-15](https://github.com/godotengine/godot/assets/3624853/ed202a55-03e8-420a-bc1c-ccfc7f7cd02a)


### Steps to reproduce

- Open a documentation page for any node
- Restart Godot

### Minimal reproduction project

NA

EDIT : Added the commit hash @Calinou 
_stop_thread();
	MutexLock data_lock(data_mutex);
	ERR_FAIL_COND(current->type == ITEM_TABLE);
	ItemColor *item = memnew(ItemColor);
	item->color = p_color;
	_add_item(item, true);
}
void RichTextLabel::push_outline_color(const Color &p_color) {
	_stop_thread();
	MutexLock data_lock(data_mutex);
	ERR_FAIL_COND(current->type == ITEM_TABLE);
	ItemOutlineColor *item = memnew(ItemOutlineColor);
	item->color = p_color;
	_add_item(item, true);
}
void RichTextLabel::push_underline() {
	_stop_thread();
	MutexLock data_lock(data_mutex);
	ERR_FAIL_COND(current->type == ITEM_TABLE);
	ItemUnderline *item = memnew(ItemUnderline);
	_add_item(item, true);
}
void RichTextLabel::push_strikethrough() {