### 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 (subtag_a[0] == "face_index" || subtag_a[0] == "fi") {
						int fi = subtag_a[1].to_int();
						fc->set_variation_face_index(fi);
					} else if (subtag_a[0] == "slant" || subtag_a[0] == "sln") {
						float slant = subtag_a[1].to_float();
						fc->set_variation_transform(Transform2D(1.0, slant, 0.0, 1.0, 0.0, 0.0));
					} else if (subtag_a[0] == "opentype_variation" || subtag_a[0] == "otv") {
						Dictionary variations;
						if (!subtag_a[1].is_empty()) {
							Vector<String> variation_tags = subtag_a[1].split(",");
							for (int j = 0; j < variation_tags.size(); j++) {
								Vector<String> subtag_b = variation_tags[j].split("=");
								_normalize_subtags(subtag_b);
								if (subtag_b.size() == 2) {
									variations[TS->name_to_tag(subtag_b[0])] = subtag_b[1].to_float();
								}
							}
							fc->set_variation_opentype(variations);
						}
					} else if (subtag_a[0] == "opentype_features" || subtag_a[0] == "otf") {
						Dictionary features;
						if (!subtag_a[1].is_empty()) {
							Vector<String> feature_tags = subtag_a[1].split(",");
							for (int j = 0; j < feature_tags.size(); j++) {
								Vector<String> subtag_b = feature_tags[j].split("=");
								_normalize_subtags(subtag_b);
								if (subtag_b.size() == 2) {
									features[TS->name_to_tag(subtag_b[0])] = subtag_b[1].to_float();
								} else if (subtag_b.size() == 1) {
									features[TS->name_to_tag(subtag_b[0])] = 1;