Reset TPS plot bottom between data sets

sohstationviewer/view/plotting/time_power_squared_dialog.py

@@ -86,6 +86,7 @@ class TimePowerSquaredWidget(plotting_widget.PlottingWidget):
         :param waveform_data: dict - read waveform data of selected data set,
             refer to DataTypeModel.__init__.waveform_data[key]['read_data']
         """
+        self.plotting_bot = const.BOTTOM
         self.processed_channels = []
         self.channels = []
         self.tps_processors = []