### 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 
ERR_FAIL_COND_V(p_frame == nullptr, false);
	ERR_FAIL_COND_V(p_line < 0 || p_line >= (int)p_frame->lines.size(), false);
	Line &l = p_frame->lines[p_line];
	String txt;
	Item *it_to = (p_line + 1 < (int)p_frame->lines.size()) ? p_frame->lines[p_line + 1].from : nullptr;
	for (Item *it = l.from; it && it != it_to; it = _get_next_item(it)) {
		switch (it->type) {
			case ITEM_NEWLINE: {
				txt += "\n";
			} break;
			case ITEM_TEXT: {
				ItemText *t = static_cast<ItemText *>(it);
				txt += t->text;
			} break;
			case ITEM_IMAGE: {
				txt += " ";
			} break;
			case ITEM_TABLE: {
				ItemTable *table = static_cast<ItemTable *>(it);