simplify condition to check show key

sohstationviewer/view/plotting/plotting_widget/multi_threaded_plotting_widget.py

@@ -187,8 +187,7 @@ class MultiThreadedPlottingWidget(PlottingWidget):
         for chan_id in chan_order:
             if 'chan_db_info' not in plotting_data[chan_id]:
                 continue
-            if ('show' in plotting_data[chan_id] and
-                    not plotting_data[chan_id]['show']):
+            if not plotting_data[chan_id].get('show'):
                 continue
             channel_processor = PlottingChannelProcessor(
                 plotting_data[chan_id], chan_id,