### 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)

font_size = font_size_it->font_size;
					}
					if (rtl) {
						stop += tab_size * font->get_char_size(' ', font_size).width;
						if (stop > p_click.x) {
							break;
						}
					} else {
						stop -= tab_size * font->get_char_size(' ', font_size).width;
						if (stop < p_click.x) {
							break;
						}
					}
					*r_click_item = _find_indentable((*r_click_item)->parent);
				}
			}
		}
		if (r_click_frame != nullptr) {
			*r_click_frame = p_frame;
		}
		if (r_click_line != nullptr) {
			*r_click_line = p_line;
		}
		if (r_click_char != nullptr) {
			*r_click_char = char_pos;
		}
	}
	return off.y;
}
void RichTextLabel::_scroll_changed(double) {