Move set_layout call

This code is identical to before, but for some reason the positioning
of this affects whether Next is the default action or not!

And it didn't have that effect with the old install wizard.  Odd.

gui/qt/installwizard.py

@@ -192,9 +192,9 @@ class InstallWizard(WindowModalDialog, MessageBoxMixin, WizardBase):
             if i==0:
                 button.setChecked(True)
 
+        self.set_layout(vbox)
         vbox.addStretch(1)
         vbox.addLayout(Buttons(CancelButton(self), OkButton(self, _('Next'))))
-        self.set_layout(vbox)
         self.show()
         self.raise_()