### 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 (column == col_count - 1 || E->next() == nullptr) {
						offset.x = 0;
						row_height += theme_cache.table_v_separation;
						table->total_height += row_height;
						offset.y += row_height;
						table->rows.push_back(row_height);
						table->rows_baseline.push_back(table->total_height - row_height + row_baseline);
						row_height = 0;
					}
					idx++;
				}
				int row_idx = (table->align_to_row < 0) ? table->rows_baseline.size() - 1 : table->align_to_row;
				if (table->rows_baseline.size() != 0 && row_idx < (int)table->rows_baseline.size() - 1) {
					l.text_buf->add_object((uint64_t)it, Size2(table->total_width, table->total_height), table->inline_align, t_char_count, Math::round(table->rows_baseline[row_idx]));
				} else {
					l.text_buf->add_object((uint64_t)it, Size2(table->total_width, table->total_height), table->inline_align, t_char_count);
				}
				txt += String::chr(0xfffc).repeat(t_char_count);
			} break;
			default:
				break;
		}
	}
	
	l.text_buf->set_bidi_override(structured_text_parser(_find_stt(l.from), st_args, txt));
	*r_char_offset = l.char_offset + l.char_count;
	l.offset.y = p_h;
	return _calculate_line_vertical_offset(l);
}
int RichTextLabel::_draw_line(ItemFrame *p_frame, int p_line, const Vector2 &p_ofs, int p_width, const Color &p_base_color, int p_outline_size, const Color &p_outline_color, const Color &p_font_shadow_color, int p_shadow_outline_size, const Point2 &p_shadow_ofs, int &r_processed_glyphs) {