remove '' chan in pref_soh_chan

sohstationviewer/view/main_window.py

@@ -894,7 +894,8 @@ class MainWindow(QtWidgets.QMainWindow, UIMainWindow):
                                'WHERE current=1')
         if len(rows) > 0:
             self.pref_soh_list_name = rows[0]['name']
-            self.pref_soh_list = [t.strip() for t in rows[0]['IDs'].split(',')]
+            self.pref_soh_list = [t.strip() for t in rows[0]['IDs'].split(',')
+                                  if t.strip() != '']
             self.pref_soh_list_data_type = rows[0]['dataType']
 
     def resizeEvent(self, event):