Describe the bug
When a folder that does not contain files but, contains one or more sub-folders that contain one or more files gets copied or moved into "PDFKeeper Upload", the Upload Directory Maintenance that executes during the upload cycle is deleting the folder and all sub-folders and files. This is a regression bug that was introduced during the first half of the VB.NET to C# migration in v9.0.0.

To Reproduce
Steps to reproduce the behavior:

1. Copy or cut and paste a folder that does not contain files but contains one or more sub-folders that contain one or more files into "PDFKeeper Upload" while PDFKeeper is open.
2. See error

Expected behavior
PDFKeeper should either upload or reject (move to UploadRejected folder) each PDF in the Upload folder and ignore any files that do not have a PDF extension.

Desktop (please complete the following information):

• PDFKeeper Version: 9.0.0 - 10.1.0