Fix file handling in 'file' field

[Former user]

Reported by dbe: The file upload seems to have problems when

• the file is written in the 'file' entry
• the file is located in JabRef's main file directory.

Please check.

Notify on complete: [e-mail].

[Former user]

Same problem for me... Files that are in the 'pdf' entry are uploaded fine, but those in the 'file' entry cause an exception ("file is not a normal file").

Best regards Philipp