Fix possible crash due to labels (closes #64)

src/transferlistfilterswidget.h

@@ -447,6 +447,8 @@ protected slots:
     if (!label.isEmpty()) {
       if (!customLabels.contains(label)) {
         addLabel(label);
+        // addLabel may have changed the label, update the model accordingly.
+        torrentItem->setData(TorrentModelItem::TR_LABEL, label);
       }
       // Update label counter
       Q_ASSERT(customLabels.contains(label));