UnauthorizedAccessException when trying to deserialize read-only files

[bburlacu]

If the file has the read-only attribute on disk then HL persistence will fail to open it and throw an exception:

HeuristicLab version: 3.3.16.17184
UnauthorizedAccessException: Access to the path 'C:\Users\P40913\Nextcloud\Work\Test.hl' is denied.
   at HeuristicLab.Optimizer.FileManager.LoadingCompleted(IStorableContent content, Exception error, Info info) in C:\Projects\hl-core\trunk\HeuristicLab.Optimizer\3.3\FileManager.cs:line 78