Temp add a frame count value display of previcwscan

src/ScanFormWidget.h

@@ -19,6 +19,7 @@ private:
     bool unset = true;
     bool previewing= false;
     std::function<void(bool)> previewfunc = nullptr;
+    int currentFrame = 0;
 private slots:
     void protocolChanged(int type);