### Godot version

4.0 RC1

### System information

Linux Mint 20.3 Cinnamon

### Issue description

Tried converting a 3.5 game to 4.0 RC1. The conversion popup menu closed after a few seconds, and trying to edit the game crashes the entire engine with the following errors, which seem to be related to one music file not loading:
![errors](https://user-images.githubusercontent.com/125468288/219127087-f5a78035-4e4a-4625-aadb-e0cde6d5ac3d.png)

Not sure what's causing the issue, because when I created a new project with only that file and converted it I didn't get these errors, but consistently get them when trying to convert that game.

### Steps to reproduce

- Download the reproduction project below
- Import in Godot 4.0, and click "convert full project"
- If the bug happens, the engine will crash whenever trying to edit or run the converted project

### Minimal reproduction project

[Music Convertor Crash Demo.zip](https://github.com/godotengine/godot/files/10746591/Music.Convertor.Crash.Demo.zip)

String empty_space;
	int current_character = 0;
	if (line.is_empty()) {
		return empty_space;
	}
	if (line[0] == ' ') {
		while (current_character < line.size()) {
			if (line[current_character] == ' ') {
				empty_space += ' ';
				current_character++;
			} else {
				break;
			}
		}
	}
	if (line[0] == '\t') {
		while (current_character < line.size()) {
			if (line[current_character] == '\t') {
				empty_space += '\t';
				current_character++;
			} else {
				break;
			}
		}
	}
	return empty_space;
}
// Returns the object that’s executing the function in the line.
// e.g. Passing the line "var roman = kieliszek.funkcja()" to this function returns "kieliszek".
String ProjectConverter3To4::get_object_of_execution(const String &line) const {