Again don't crash on zero size attachments.
Again don't crash on zero size attachments.

svn path=/trunk/kdenetwork/kmail/; revision=131487

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