### 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 (in_bold) {
				_push_def_font(BOLD_ITALICS_FONT);
			} else {
				_push_def_font(ITALICS_FONT);
			}
			pos = brk_end + 1;
			tag_stack.push_front(tag);
		} else if (tag == "code") {
			
			_push_def_font(MONO_FONT);
			pos = brk_end + 1;
			tag_stack.push_front(tag);
		} else if (tag.begins_with("table=")) {
			Vector<String> subtag = tag.substr(6, tag.length()).split(",");
			_normalize_subtags(subtag);
			int columns = subtag[0].to_int();
			if (columns < 1) {
				columns = 1;
			}
			int alignment = INLINE_ALIGNMENT_TOP;
			if (subtag.size() > 2) {
				if (subtag[1] == "top" || subtag[1] == "t") {
					alignment = INLINE_ALIGNMENT_TOP_TO;
				} else if (subtag[1] == "center" || subtag[1] == "c") {
					alignment = INLINE_ALIGNMENT_CENTER_TO;
				} else if (subtag[1] == "baseline" || subtag[1] == "l") {
					alignment = INLINE_ALIGNMENT_BASELINE_TO;
				} else if (subtag[1] == "bottom" || subtag[1] == "b") {
					alignment = INLINE_ALIGNMENT_BOTTOM_TO;
				}