### 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)

static String error_message = "The master and mastersync rpc behavior is not officially supported anymore. Try using another keyword or making custom logic using Multiplayer.GetRemoteSenderId()\n";
	for (SourceLine &source_line : source_lines) {
		if (source_line.is_comment) {
			continue;
		}
		String &line = source_line.line;
		if (uint64_t(line.length()) <= maximum_line_length) {
			line = reg_container.keyword_csharp_remote.sub(line, "[RPC(MultiplayerAPI.RPCMode.AnyPeer)]", true);
			line = reg_container.keyword_csharp_remotesync.sub(line, "[RPC(MultiplayerAPI.RPCMode.AnyPeer, CallLocal = true)]", true);
			line = reg_container.keyword_csharp_puppet.sub(line, "[RPC]", true);
			line = reg_container.keyword_csharp_puppetsync.sub(line, "[RPC(CallLocal = true)]", true);
			line = reg_container.keyword_csharp_master.sub(line, error_message + "[RPC]", true);
			line = reg_container.keyword_csharp_mastersync.sub(line, error_message + "[RPC(CallLocal = true)]", true);
		}
	}
}
Vector<String> ProjectConverter3To4::check_for_rename_csharp_attributes(Vector<String> &lines, const RegExContainer &reg_container) {
	int current_line = 1;
	Vector<String> found_renames;
	for (String &line : lines) {
		if (uint64_t(line.length()) <= maximum_line_length) {
			String old;
			old = line;
			line = reg_container.keyword_csharp_remote.sub(line, "[RPC(MultiplayerAPI.RPCMode.AnyPeer)]", true);
			if (old != line) {
				found_renames.append(line_formatter(current_line, "[Remote]", "[RPC(MultiplayerAPI.RPCMode.AnyPeer)]", line));
			}
			old = line;