Stop KMSearch::slotProcessNextBatch crashing on some invalid serNums.
Stop KMSearch::slotProcessNextBatch crashing on some invalid serNums.

svn path=/trunk/kdenetwork/kmail/; revision=196432

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