### 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)

if (p_name == "bbcode_text" && !((String)p_value).is_empty()) {
		set_text(p_value);
		return true;
	}
	return false;
}
#endif
void RichTextLabel::_bind_methods() {
	ClassDB::bind_method(D_METHOD("get_parsed_text"), &RichTextLabel::get_parsed_text);
	ClassDB::bind_method(D_METHOD("add_text", "text"), &RichTextLabel::add_text);
	ClassDB::bind_method(D_METHOD("set_text", "text"), &RichTextLabel::set_text);
	ClassDB::bind_method(D_METHOD("add_image", "image", "width", "height", "color", "inline_align", "region"), &RichTextLabel::add_image, DEFVAL(0), DEFVAL(0), DEFVAL(Color(1.0, 1.0, 1.0)), DEFVAL(INLINE_ALIGNMENT_CENTER), DEFVAL(Rect2(0, 0, 0, 0)));
	ClassDB::bind_method(D_METHOD("newline"), &RichTextLabel::add_newline);
	ClassDB::bind_method(D_METHOD("remove_paragraph", "paragraph"), &RichTextLabel::remove_paragraph);
	ClassDB::bind_method(D_METHOD("push_font", "font", "font_size"), &RichTextLabel::push_font, DEFVAL(0));
	ClassDB::bind_method(D_METHOD("push_font_size", "font_size"), &RichTextLabel::push_font_size);
	ClassDB::bind_method(D_METHOD("push_normal"), &RichTextLabel::push_normal);
	ClassDB::bind_method(D_METHOD("push_bold"), &RichTextLabel::push_bold);
	ClassDB::bind_method(D_METHOD("push_bold_italics"), &RichTextLabel::push_bold_italics);
	ClassDB::bind_method(D_METHOD("push_italics"), &RichTextLabel::push_italics);
	ClassDB::bind_method(D_METHOD("push_mono"), &RichTextLabel::push_mono);