### 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 (String &subtag : subtags) {
		subtag = subtag.unquote();
	}
}
bool RichTextLabel::_find_meta(Item *p_item, Variant *r_meta, ItemMeta **r_item) {
	Item *item = p_item;
	while (item) {
		if (item->type == ITEM_META) {
			ItemMeta *meta = static_cast<ItemMeta *>(item);
			if (r_meta) {
				*r_meta = meta->meta;
			}
			if (r_item) {
				*r_item = meta;
			}
			return true;
		}
		item = item->parent;
	}
	return false;
}
bool RichTextLabel::_find_hint(Item *p_item, String *r_description) {