### 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)

int current_line = 1;
	Vector<String> found_renames;
	for (String &line : lines) {
		if (uint64_t(line.length()) <= maximum_line_length) {
			String old_line = line;
			process_gdscript_line(line, reg_container, builtin);
			if (old_line != line) {
				found_renames.append(simple_line_formatter(current_line, old_line, line));
			}
		}
	}
	return found_renames;
}
bool ProjectConverter3To4::contains_function_call(String &line, String function) const {
	// 
	// 
	if (!line.contains(function)) {
		return false;
	}
	int index = line.find(function);
	if (index == 0) {
		return true;
	}
	char32_t previous_char = line.get(index - 1);
	return (previous_char < '0' || previous_char > '9') && (previous_char < 'a' || previous_char > 'z') && (previous_char < 'A' || previous_char > 'Z') && previous_char != '_' && previous_char != '$' && previous_char != '@';
}
, this function should run only on all ".gd" files and also on lines in ".tscn" files which are parts of built-in Scripts.
void ProjectConverter3To4::process_gdscript_line(String &line, const RegExContainer &reg_container, bool builtin) {