### 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)

return progress_delay;
}
_FORCE_INLINE_ float RichTextLabel::_update_scroll_exceeds(float p_total_height, float p_ctrl_height, float p_width, int p_idx, float p_old_scroll, float p_text_rect_height) {
	updating_scroll = true;
	float total_height = p_total_height;
	bool exceeds = p_total_height > p_ctrl_height && scroll_active;
	if (exceeds != scroll_visible) {
		if (exceeds) {
			scroll_visible = true;
			scroll_w = vscroll->get_combined_minimum_size().width;
			vscroll->show();
			vscroll->set_anchor_and_offset(SIDE_LEFT, ANCHOR_END, -scroll_w);
		} else {
			scroll_visible = false;
			scroll_w = 0;
			vscroll->hide();
		}
		main->first_resized_line.store(0);
		total_height = 0;
		for (int j = 0; j <= p_idx; j++) {
			total_height = _resize_line(main, j, theme_cache.normal_font, theme_cache.normal_font_size, p_width - scroll_w, total_height);
			main->first_resized_line.store(j);
		}
	}
	vscroll->set_max(total_height);
	vscroll->set_page(p_text_rect_height);
	if (scroll_follow && scroll_following) {
		vscroll->set_value(total_height);
	} else {
		vscroll->set_value(p_old_scroll);