### 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 expected = "r.";
	String got = get_object_of_execution(base);
	if (got != expected) {
		ERR_PRINT(vformat("Failed to get proper data from get_object_of_execution. \"%s\" should return \"%s\"(%d), got \"%s\"(%d), instead.", base, expected, expected.size(), got, got.size()));
	}
	valid = valid && (got == expected);
}
{
	String base = "mortadela(";
	String expected = "";
	String got = get_object_of_execution(base);
	if (got != expected) {
		ERR_PRINT(vformat("Failed to get proper data from get_object_of_execution. \"%s\" should return \"%s\"(%d), got \"%s\"(%d), instead.", base, expected, expected.size(), got, got.size()));
	}
	valid = valid && (got == expected);
}
{
	String base = "var node = $world/ukraine/lviv.";
	String expected = "$world/ukraine/lviv.";
	String got = get_object_of_execution(base);
	if (got != expected) {
		ERR_PRINT(vformat("Failed to get proper data from get_object_of_execution. \"%s\" should return \"%s\"(%d), got \"%s\"(%d), instead.", base, expected, expected.size(), got, got.size()));
	}
	valid = valid && (got == expected);
}
}
{
	String base = "\t\t\t var roman = kieliszek.";
	String expected = "\t\t\t";
	String got = get_starting_space(base);