Zero out mApplyThemeColumnsTimer so Model will not cause accesses to it in its destruction process. Fixes kontact/kmail crashing on  exit.
Zero out mApplyThemeColumnsTimer so Model will not cause accesses to it in its destruction process. Fixes kontact/kmail crashing on 
exit.

svn path=/trunk/KDE/kdepim/; revision=895052

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