### 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 table_offy;
		}
		off.y += TS->shaped_text_get_descent(rid) + theme_cache.line_separation;
	}
	
	if (line_clicked) {
		
		if (r_click_item != nullptr) {
			Item *it = p_frame->lines[p_line].from;
			Item *it_to = (p_line + 1 < (int)p_frame->lines.size()) ? p_frame->lines[p_line + 1].from : nullptr;
			if (char_pos >= 0) {
				*r_click_item = _get_item_at_pos(it, it_to, char_pos);
			} else {
				int stop = text_rect_begin;
				*r_click_item = _find_indentable(it);
				while (*r_click_item) {
					Ref<Font> font = theme_cache.normal_font;
					int font_size = theme_cache.normal_font_size;
					ItemFont *font_it = _find_font(*r_click_item);
					if (font_it) {
						if (font_it->font.is_valid()) {
							font = font_it->font;
						}
						if (font_it->font_size > 0) {
							font_size = font_it->font_size;
						}
					}
					ItemFontSize *font_size_it = _find_font_size(*r_click_item);
					if (font_size_it && font_size_it->font_size > 0) {