Gui: [skip ci] fix warning when opening preferences dialog in debug mode

The warning is e.g.: QWindowsWindow::setGeometry: Unable to set geometry 570x454+1524+350 on QWidgetWindow/'Gui__Dialog__DlgPreferencesWindow

src/Gui/DlgPreferencesImp.cpp

@@ -303,6 +303,7 @@ void DlgPreferencesImp::applyChanges()
 void DlgPreferencesImp::showEvent(QShowEvent* ev)
 {
     //canEmbedScrollArea = false;
+    this->adjustSize();
     QDialog::showEvent(ev);
 }