Fix a crahs when the "filename" parameter to Content-disposition was empty like so: "filename=".
Fix a crahs when the "filename" parameter to Content-disposition was
empty like so: "filename=".

svn path=/trunk/kdenetwork/kmail/; revision=103796

lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi