### 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)

pos = brk_end + 1;
			tag_stack.push_front("ol");
		} else if (tag == "ol type=a") {
			indent_level++;
			push_list(indent_level, LIST_LETTERS, false);
			pos = brk_end + 1;
			tag_stack.push_front("ol");
		} else if (tag == "ol type=A") {
			indent_level++;
			push_list(indent_level, LIST_LETTERS, true);
			pos = brk_end + 1;
			tag_stack.push_front("ol");
		} else if (tag == "ol type=i") {
			indent_level++;
			push_list(indent_level, LIST_ROMAN, false);
			pos = brk_end + 1;
			tag_stack.push_front("ol");
		} else if (tag == "ol type=I") {
			indent_level++;
			push_list(indent_level, LIST_ROMAN, true);
			pos = brk_end + 1;
			tag_stack.push_front("ol");
		} else if (tag == "indent") {
			indent_level++;
			push_indent(indent_level);
			pos = brk_end + 1;
			tag_stack.push_front(tag);
		} else if (tag == "p") {
			push_paragraph(HORIZONTAL_ALIGNMENT_LEFT);
			pos = brk_end + 1;