Backport commit 1154472.
Backport commit 1154472.

Fix crash on setting default button.

svn path=/branches/KDE/4.4/kdepim/; revision=1171647

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