Fix shared docs zip upload to send multiple files at once
Created by: ldidry
On Debian 9, with perl 5.24.1 and Archive::Zip 1.59 and 1.64, uploading a zip file to let Sympa (6.2.34) unzip it and put its files into shared docs fails. The zip member is a CGI::File::Temp instance and can seek but fails to be extracted ("Unable to extract member XXX of the zip file" in Sympa logs). Unconditionnally blessing the file handle to IO::File fixes the failure.