Fix a crash bug - if the contact list is sorted on the rightmost column, then you remove that field in Modify View, we still try to sort on that column, and our reimplementation of LVI::key() did not return QString::null for nonexistent columns.
Fix a crash bug - if the contact list is sorted on the rightmost column, then you remove that field in Modify View, we still try to sort on that column, and our reimplementation of LVI::key() did not return QString::null for nonexistent columns.

svn path=/trunk/kdepim/; revision=318909

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