If GPS Lk/Unlk not exist, error will happen.

If the channel listed in linkedChan not exist, error will happen. Need to fix this. recommend fix:

should change code in state_of health widget.plot_single_channel to this.

        try:
            if chan_db_info['linkedChan'] not in [None, 'None', '']:
                linked_ax = self.plotting_data1[chan_db_info[
                    'linkedChan']]['ax']
        except KeyError:
            pass

exp: 2013326.9E4A