add back clearDeviceOptions for KSaneWidget

got lost during the KSaneCore/KSaneWidget split

src/ksanewidget.cpp

@@ -367,7 +367,7 @@ bool KSaneWidget::closeDevice()
     if (!result) {
         return false;
     }
- 
+    d->clearDeviceOptions();
     // disable the interface until a new device is opened.
     d->m_optsTabWidget->setDisabled(true);
     d->m_previewViewer->setDisabled(true);

src/ksanewidget_p.cpp

@@ -116,7 +116,7 @@ void KSaneWidgetPrivate::clearDeviceOptions()
     
     m_handledOptions.clear();
 
-    // remove the remaining layouts/widgets and read thread
+    // remove the remaining layouts/widgets
     delete m_basicOptsTab;
     m_basicOptsTab = nullptr;