When I try to import PDFs via the Quality -> Find unlinked files, the process freezes when a PDF containing a curly bracket ( "{" or "}" ) in its filename is encountered.

JabRef version 4.0.0-dev (snapshot 2017-02-18) on Win 10 (1607)

Steps to reproduce:

1. Open Quality -> Find unlinked files
2. Select a folder containing at least one PDF with a curly bracket in its name
3. Scan directory
4. Make sure the offending file is selected
5. Apply

After the last step, the process goes through all valid files (showing "Importing into database... M of N"), but freezes the whole JabRef once it gets to the offending file.