### 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 visible_characters;
}
int RichTextLabel::get_character_line(int p_char) {
	_validate_line_caches();
	int line_count = 0;
	int to_line = main->first_invalid_line.load();
	for (int i = 0; i < to_line; i++) {
		MutexLock lock(main->lines[i].text_buf->get_mutex());
		if (main->lines[i].char_offset < p_char && p_char <= main->lines[i].char_offset + main->lines[i].char_count) {
			for (int j = 0; j < main->lines[i].text_buf->get_line_count(); j++) {
				Vector2i range = main->lines[i].text_buf->get_line_range(j);
				if (main->lines[i].char_offset + range.x < p_char && p_char <= main->lines[i].char_offset + range.y) {
					return line_count;
				}
				line_count++;
			}
		} else {
			line_count += main->lines[i].text_buf->get_line_count();
		}
	}
	return -1;
}
int RichTextLabel::get_character_paragraph(int p_char) {