### 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)

ClassDB::bind_method(D_METHOD("set_text_direction", "direction"), &RichTextLabel::set_text_direction);
	ClassDB::bind_method(D_METHOD("get_text_direction"), &RichTextLabel::get_text_direction);
	ClassDB::bind_method(D_METHOD("set_language", "language"), &RichTextLabel::set_language);
	ClassDB::bind_method(D_METHOD("get_language"), &RichTextLabel::get_language);
	ClassDB::bind_method(D_METHOD("set_autowrap_mode", "autowrap_mode"), &RichTextLabel::set_autowrap_mode);
	ClassDB::bind_method(D_METHOD("get_autowrap_mode"), &RichTextLabel::get_autowrap_mode);
	ClassDB::bind_method(D_METHOD("set_meta_underline", "enable"), &RichTextLabel::set_meta_underline);
	ClassDB::bind_method(D_METHOD("is_meta_underlined"), &RichTextLabel::is_meta_underlined);
	ClassDB::bind_method(D_METHOD("set_hint_underline", "enable"), &RichTextLabel::set_hint_underline);
	ClassDB::bind_method(D_METHOD("is_hint_underlined"), &RichTextLabel::is_hint_underlined);
	ClassDB::bind_method(D_METHOD("set_scroll_active", "active"), &RichTextLabel::set_scroll_active);
	ClassDB::bind_method(D_METHOD("is_scroll_active"), &RichTextLabel::is_scroll_active);
	ClassDB::bind_method(D_METHOD("set_scroll_follow", "follow"), &RichTextLabel::set_scroll_follow);
	ClassDB::bind_method(D_METHOD("is_scroll_following"), &RichTextLabel::is_scroll_following);
	ClassDB::bind_method(D_METHOD("get_v_scroll_bar"), &RichTextLabel::get_v_scroll_bar);
	ClassDB::bind_method(D_METHOD("scroll_to_line", "line"), &RichTextLabel::scroll_to_line);
	ClassDB::bind_method(D_METHOD("scroll_to_paragraph", "paragraph"), &RichTextLabel::scroll_to_paragraph);
	ClassDB::bind_method(D_METHOD("scroll_to_selection"), &RichTextLabel::scroll_to_selection);
	ClassDB::bind_method(D_METHOD("set_tab_size", "spaces"), &RichTextLabel::set_tab_size);
	ClassDB::bind_method(D_METHOD("get_tab_size"), &RichTextLabel::get_tab_size);
	ClassDB::bind_method(D_METHOD("set_fit_content", "enabled"), &RichTextLabel::set_fit_content);
	ClassDB::bind_method(D_METHOD("is_fit_content_enabled"), &RichTextLabel::is_fit_content_enabled);
	ClassDB::bind_method(D_METHOD("set_selection_enabled", "enabled"), &RichTextLabel::set_selection_enabled);
	ClassDB::bind_method(D_METHOD("is_selection_enabled"), &RichTextLabel::is_selection_enabled);
	ClassDB::bind_method(D_METHOD("set_context_menu_enabled", "enabled"), &RichTextLabel::set_context_menu_enabled);
	ClassDB::bind_method(D_METHOD("is_context_menu_enabled"), &RichTextLabel::is_context_menu_enabled);
	ClassDB::bind_method(D_METHOD("set_shortcut_keys_enabled", "enabled"), &RichTextLabel::set_shortcut_keys_enabled);
	ClassDB::bind_method(D_METHOD("is_shortcut_keys_enabled"), &RichTextLabel::is_shortcut_keys_enabled);
	ClassDB::bind_method(D_METHOD("set_deselect_on_focus_loss_enabled", "enable"), &RichTextLabel::set_deselect_on_focus_loss_enabled);
	ClassDB::bind_method(D_METHOD("is_deselect_on_focus_loss_enabled"), &RichTextLabel::is_deselect_on_focus_loss_enabled);