since when is not visible the dialog doesn't update its size
from the mainItem size, the minimum size should not be
updated as well, or the initial mainitem size will get lost
and the dialog will be initialized to a wrong size
Patch by: Vishesh Handa <vhanda@kde.org>
Change-Id: I272727fb4732474b102de64c9bfdddb7fc3906c8
