fix: crash on startup when working directory is root

[iedame]

Steps to reproduce

cd /
/path/to/Helion

On macOS this also happens whenever Helion is launched from an .app bundle

(Finder/Launchpad), because the working directory is / in that case.

Result

System.ArgumentException: The value cannot be an empty string. (Parameter 'path')
   at System.ArgumentException.ThrowNullOrEmptyException(String, String) + 0x40
   at System.IO.Path.GetFullPath(String) + 0x4c
   at Helion.Util.PathsManager.StandardizePath(String path) + 0x10
   at System.Linq.Enumerable.SizeOptIListSelectIterator`2.MoveNext() + 0x90
   at System.Linq.Enumerable.DistinctIterator`1.MoveNext() + 0x64
   at System.Collections.Generic.List`1..ctor(IEnumerable`1) + 0x90
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1) + 0x30
   at Helion.Resources.Archives.Locator.FilesystemArchiveLocator..ctor(PathsManager, IConfig, IList`1) + 0x54
   at Helion.Client.Client.Run(CommandLineArgs commandLineArgs, PathsManager pathsManager) + 0xfc

Cause

PathsManager.StandardizePath does Path.GetFullPath(path).TrimEnd(Path.DirectorySeparatorChar)
For / this trims the whole string, so the launch folder becomes ""
GetArchiveFolders later passes it through StandardizePath again, and Path.GetFullPath("") throws

With this change Helion starts normally from / and from an app bundle.
Found while packaging Helion for nixpkgs (NixOS/nixpkgs#554503) and confirmed the crash is reproducible on both macOS and linux, works as expected after applying patch.