### 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)

table->columns[i].expand = true;
					}
					if (table->columns[i].expand) {
						total_ratio += table->columns[i].expand_ratio;
					}
				}
				
				for (int i = 0; i < col_count; i++) {
					table->columns[i].width = table->columns[i].min_width;
					if (table->columns[i].expand && total_ratio > 0 && remaining_width > 0) {
						table->columns[i].width += table->columns[i].expand_ratio * remaining_width / total_ratio;
					}
					if (i != col_count - 1) {
						table->total_width += table->columns[i].width + theme_cache.table_h_separation;
					} else {
						table->total_width += table->columns[i].width;
					}
				}
				
				bool table_need_fit = true;
				while (table_need_fit) {
					table_need_fit = false;
					
					for (int i = 0; i < col_count; i++) {
						if (!table->columns[i].expand) {
							continue;
						}
						int dif = table->columns[i].width - table->columns[i].max_width;
						if (dif > 0) {
							table_need_fit = true;