BUG: Fixed bug when scrolling below the 0th slice

Libs/DICOM/Widgets/ctkDICOMAppWidget.cpp

@@ -211,6 +211,7 @@ void ctkDICOMAppWidget::onDICOMModelSelected(const QModelIndex& index)
   {
     DicomImage dcmImage( thumbnailPath.toStdString().c_str() );
     ctkDICOMImage ctkImage( & dcmImage );
+    d->imagePreview->clearImages();
     d->imagePreview->addImage( ctkImage );
   }
   else

Libs/Widgets/ctkQImageView.cpp

@@ -311,7 +311,8 @@ double ctkQImageView::yCenter( void )
 void ctkQImageView::setSliceNumber( int slicenum )
 {
   Q_D( ctkQImageView );
-  if( slicenum < d->ImageList.size() && slicenum != d->SliceNumber )
+  if( slicenum >= 0 && slicenum < d->ImageList.size() 
+    && slicenum != d->SliceNumber )
     {
     d->SliceNumber = slicenum;
     emit this->sliceNumberChanged( slicenum );