[OWViewer] fix: viewer was still pending

orangecontrib/tomwer/widgets/visualization/DataViewerOW.py

@@ -98,3 +98,8 @@ class DataViewerOW(widget.OWWidget):
         if 'radio_opt' in settings:
             self.viewer.setRadioOption(settings['radio_opt'])
         self.viewer.blockSignals(old_state)
+
+    def close(self):
+        self.viewer.close()
+        self.viewer = None
+        super().close()