### 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 if (tag == "center") {
			push_paragraph(HORIZONTAL_ALIGNMENT_CENTER);
			pos = brk_end + 1;
			tag_stack.push_front(tag);
		} else if (tag == "fill") {
			push_paragraph(HORIZONTAL_ALIGNMENT_FILL);
			pos = brk_end + 1;
			tag_stack.push_front(tag);
		} else if (tag == "left") {
			push_paragraph(HORIZONTAL_ALIGNMENT_LEFT);
			pos = brk_end + 1;
			tag_stack.push_front(tag);
		} else if (tag == "right") {
			push_paragraph(HORIZONTAL_ALIGNMENT_RIGHT);
			pos = brk_end + 1;
			tag_stack.push_front(tag);
		} else if (tag == "ul") {
			indent_level++;
			push_list(indent_level, LIST_DOTS, false);
			pos = brk_end + 1;
			tag_stack.push_front(tag);
		} else if (tag.begins_with("ul bullet=")) {
			String bullet = tag.substr(10, 1);
			indent_level++;
			push_list(indent_level, LIST_DOTS, false, bullet);
			pos = brk_end + 1;
			tag_stack.push_front("ul");
		} else if ((tag == "ol") || (tag == "ol type=1")) {
			indent_level++;
			push_list(indent_level, LIST_NUMBERS, false);