### 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)

bool skip = (trim_chars && l.char_offset + glyphs[i].end > visible_characters) || (trim_glyphs_ltr && (r_processed_glyphs >= visible_glyphs)) || (trim_glyphs_rtl && (r_processed_glyphs < total_glyphs - visible_glyphs));
				if (txt_visible) {
					if (!skip) {
						if (frid != RID()) {
							TS->font_draw_glyph(frid, ci, glyphs[i].font_size, p_ofs + fx_offset + off, gl, font_color);
						} else if (((glyphs[i].flags & TextServer::GRAPHEME_IS_VIRTUAL) != TextServer::GRAPHEME_IS_VIRTUAL) && ((glyphs[i].flags & TextServer::GRAPHEME_IS_EMBEDDED_OBJECT) != TextServer::GRAPHEME_IS_EMBEDDED_OBJECT)) {
							TS->draw_hex_code_box(ci, glyphs[i].font_size, p_ofs + fx_offset + off, gl, font_color);
						}
					}
					r_processed_glyphs++;
				}
				if (skip) {
					
					if (ul_started) {
						ul_started = false;
						float y_off = TS->shaped_text_get_underline_position(rid);
						float underline_width = MAX(1.0, TS->shaped_text_get_underline_thickness(rid) * theme_cache.base_scale);
						draw_line(ul_start + Vector2(0, y_off), p_ofs + Vector2(off.x, off.y + y_off), ul_color, underline_width);
					}
					if (dot_ul_started) {
						dot_ul_started = false;
						float y_off = TS->shaped_text_get_underline_position(rid);
						float underline_width = MAX(1.0, TS->shaped_text_get_underline_thickness(rid) * theme_cache.base_scale);
						draw_dashed_line(dot_ul_start + Vector2(0, y_off), p_ofs + Vector2(off.x, off.y + y_off), dot_ul_color, underline_width, MAX(2.0, underline_width * 2));
					}
					if (st_started) {
						st_started = false;
						float y_off = -TS->shaped_text_get_ascent(rid) + TS->shaped_text_get_size(rid).y / 2;
						float underline_width = MAX(1.0, TS->shaped_text_get_underline_thickness(rid) * theme_cache.base_scale);
						draw_line(st_start + Vector2(0, y_off), p_ofs + Vector2(off.x, off.y + y_off), st_color, underline_width);