Fix WebDAV file upload on Mac when the file name contains double byte character

Steps to reproduce:

1. Use an Apple computer
2. Locally create a file whose name is télé.java and copy it
3. Connect to Nuxeo with a WebDAV drive
4. Paste the local file télé.java in a folder of the WebDAV drive
5. 2 documents are created in the Nuxeo repository, one with a size of 0 byte, one with the expected size

Expected behavior: only one document with the expected size must be created in the repository

Reproduced on LTS 2015 with nuxeo-7.10-HF38 installed