### Godot version

v4.0.2.stable.official [7a0977ce2]

### System information

Windows 10, not platform specific

### Issue description

Methods `get_character_line` and `get_character_paragraph` return wrong indices for characters that are first in the respective line/paragraph. See the attached screenshot.

![image](https://user-images.githubusercontent.com/892180/236546781-692603be-eb09-419e-822e-d4152a66d9b6.png)


### Steps to reproduce

Run attached project.

The script goes through all characters in `RichTextLabel` and prints the respective character, line index, and paragraph index. None of them should be -1 since we are iterating through valid indices.

### Minimal reproduction project

[RichTextLabel.zip](https://github.com/godotengine/godot/files/11409399/RichTextLabel.zip)

_invalidate_current_line(current_frame);
	if (fit_content) {
		update_minimum_size();
	}
	queue_redraw();
}
void RichTextLabel::_remove_item(Item *p_item, const int p_line, const int p_subitem_line) {
	int size = p_item->subitems.size();
	if (size == 0) {
		p_item->parent->subitems.erase(p_item);
		
		if (p_item->type == ITEM_NEWLINE) {
			current_frame->lines.remove_at(p_line);
			for (int i = 0; i < current->subitems.size(); i++) {
				if (current->subitems[i]->line > p_subitem_line) {
					current->subitems[i]->line--;
				}
			}
		}
	} else {
		
		for (int i = 0; i < size; i++) {
			_remove_item(p_item->subitems.front()->get(), p_line, p_subitem_line);
		}
		
		p_item->parent->subitems.erase(p_item);
	}
	memdelete(p_item);
}
void RichTextLabel::add_image(const Ref<Texture2D> &p_image, const int p_width, const int p_height, const Color &p_color, InlineAlignment p_alignment, const Rect2 &p_region) {