### 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)

}
				} else {
					OptionMap::Iterator width_option = bbcode_options.find("width");
					if (width_option) {
						width = width_option->value.to_int();
					}
					OptionMap::Iterator height_option = bbcode_options.find("height");
					if (height_option) {
						height = height_option->value.to_int();
					}
				}
				add_image(texture, width, height, color, (InlineAlignment)alignment, region);
			}
			pos = end;
			tag_stack.push_front(bbcode_name);
		} else if (tag.begins_with("color=")) {
			String color_str = tag.substr(6, tag.length()).unquote();
			Color color = Color::from_string(color_str, theme_cache.default_color);
			push_color(color);
			pos = brk_end + 1;
			tag_stack.push_front("color");
		} else if (tag.begins_with("outline_color=")) {
			String color_str = tag.substr(14, tag.length()).unquote();
			Color color = Color::from_string(color_str, theme_cache.default_color);
			push_outline_color(color);
			pos = brk_end + 1;
			tag_stack.push_front("outline_color");
		} else if (tag.begins_with("font_size=")) {
			int fnt_size = tag.substr(10, tag.length()).to_int();
			push_font_size(fnt_size);