### 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)

print_line("Starting checking if project conversion can be done.");
	uint64_t conversion_start_time = Time::get_singleton()->get_ticks_msec();
	RegExContainer reg_container = RegExContainer();
	int cached_maximum_line_length = maximum_line_length;
	maximum_line_length = 10000; 
	ERR_FAIL_COND_V_MSG(!test_array_names(), false, "Cannot start converting due to problems with data in arrays.");
	ERR_FAIL_COND_V_MSG(!test_conversion(reg_container), false, "Aborting conversion due to validation tests failing");
	maximum_line_length = cached_maximum_line_length;
	
	
	{
		String conventer_text = "; Project was converted by built-in tool to Godot 4.0";
		ERR_FAIL_COND_V_MSG(!FileAccess::exists("project.godot"), false, "Current directory doesn't contain any Godot 3 project");
		Error err = OK;
		String project_godot_content = FileAccess::get_file_as_string("project.godot", &err);
		ERR_FAIL_COND_V_MSG(err != OK, false, "Failed to read content of \"project.godot\" file.");
		ERR_FAIL_COND_V_MSG(project_godot_content.contains(conventer_text), false, "Project already was converted with this tool.");
	}
	Vector<String> collected_files = check_for_files();
	uint32_t converted_files = 0;
	
	for (int i = 0; i < collected_files.size(); i++) {
		String file_name = collected_files[i];
		Vector<String> lines;
		uint32_t ignored_lines = 0;
		uint64_t file_size = 0;
		{
			Ref<FileAccess> file = FileAccess::open(file_name, FileAccess::READ);