Add workaround for OneDrive cloud-only files on Windows

[facboy]

could try reading the FileAttributes from the windows APIs but that adds a lot of complication. this is simple and it seems to work for me.

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[gilbertchen]

This pull request has been mentioned on Duplicacy Forum. There might be relevant details there:

https://forum.duplicacy.com/t/sporadic-failures-backing-up-from-onedrive-folder/8315/6