### 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)

line = reg_container.reg_setget_set.sub(line, "var $1$2: set = $3", true);
	}
	// 
	if (line.contains("setget")) {
		line = reg_container.reg_setget_get.sub(line, "var $1$2: get = $3", true);
	}
	if (line.contains("window_resizable")) {
		// 
		line = reg_container.reg_os_set_window_resizable.sub(line, "get_window().unresizable = not ($1)", true);
		// 
		line = reg_container.reg_os_assign_window_resizable.sub(line, "get_window().unresizable = not ($1)", true);
		// 
		line = reg_container.reg_os_is_window_resizable.sub(line, "(not get_window().unresizable)", true);
	}
	if (line.contains("window_fullscreen")) {
		// 
		line = reg_container.reg_os_set_fullscreen.sub(line, "get_window().mode = Window.MODE_EXCLUSIVE_FULLSCREEN if ($1) else Window.MODE_WINDOWED", true);
		// 
		line = reg_container.reg_os_assign_fullscreen.sub(line, "get_window().mode = Window.MODE_EXCLUSIVE_FULLSCREEN if ($1) else Window.MODE_WINDOWED", true);
		// 
		line = reg_container.reg_os_is_fullscreen.sub(line, "((get_window().mode == Window.MODE_EXCLUSIVE_FULLSCREEN) or (get_window().mode == Window.MODE_FULLSCREEN))", true);
	}
	if (line.contains("window_maximized")) {
		// 
		line = reg_container.reg_os_set_maximized.sub(line, "get_window().mode = Window.MODE_MAXIMIZED if ($1) else Window.MODE_WINDOWED", true);
		// 
		line = reg_container.reg_os_assign_maximized.sub(line, "get_window().mode = Window.MODE_MAXIMIZED if ($1) else Window.MODE_WINDOWED", true);
		// 
		line = reg_container.reg_os_is_maximized.sub(line, "(get_window().mode == Window.MODE_MAXIMIZED)", true);
	}