Fixed crash condition in ExtDate::fromString(QString, QDateFormat).

Fixed crash condition in ExtDate::fromString(QString, QDateFormat).
When using the TextFormat QDateFormat, the code creates a QStringList
from the space-separated fields of the input string, but it then assumed
that the stringlist contains at least three members, which caused a
crash when this was not the case.  Now, it will return an invalid
ExtDate if the stringlist contains fewer than three members.

Thanks for the tip, Jasem.

CCMAIL: kde-edu@kde.org
CCMAIL: kstars-devel@kde.org

svn path=/trunk/KDE/kdeedu/libkdeedu/; revision=584944