### 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)

}
				}
				off.x += glyphs[i].advance;
			}
		}
		if (ul_started) {
			ul_started = false;
			float y_off = TS->shaped_text_get_underline_position(rid);
			float underline_width = MAX(1.0, TS->shaped_text_get_underline_thickness(rid) * theme_cache.base_scale);
			draw_line(ul_start + Vector2(0, y_off), p_ofs + Vector2(off.x, off.y + y_off), ul_color, underline_width);
		}
		if (dot_ul_started) {
			dot_ul_started = false;
			float y_off = TS->shaped_text_get_underline_position(rid);
			float underline_width = MAX(1.0, TS->shaped_text_get_underline_thickness(rid) * theme_cache.base_scale);
			draw_dashed_line(dot_ul_start + Vector2(0, y_off), p_ofs + Vector2(off.x, off.y + y_off), dot_ul_color, underline_width, MAX(2.0, underline_width * 2));
		}
		if (st_started) {
			st_started = false;
			float y_off = -TS->shaped_text_get_ascent(rid) + TS->shaped_text_get_size(rid).y / 2;
			float underline_width = MAX(1.0, TS->shaped_text_get_underline_thickness(rid) * theme_cache.base_scale);
			draw_line(st_start + Vector2(0, y_off), p_ofs + Vector2(off.x, off.y + y_off), st_color, underline_width);
		}
		
		_draw_fbg_boxes(ci, rid, fbg_line_off, it_from, it_to, chr_range.x, chr_range.y, 1);
		off.y += TS->shaped_text_get_descent(rid);
	}
	return line_count;
}
void RichTextLabel::_find_click(ItemFrame *p_frame, const Point2i &p_click, ItemFrame **r_click_frame, int *r_click_line, Item **r_click_item, int *r_click_char, bool *r_outside, bool p_meta) {