### 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)

for (int i = 0; i < custom_effects.size(); i++) {
		Ref<RichTextEffect> effect = custom_effects[i];
		if (!effect.is_valid()) {
			continue;
		}
		if (effect->get_bbcode() == p_bbcode_identifier) {
			return effect;
		}
	}
	return Ref<RichTextEffect>();
}
Dictionary RichTextLabel::parse_expressions_for_values(Vector<String> p_expressions) {