Avoid a QDateTime warning when trying to call fromString on "".
Avoid a QDateTime warning when trying to call fromString on "".

svn path=/branches/kdepim/proko2/kdepim/; revision=412105

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