Fix previous plot still showing when re-plotting after zooming in

Closes #95 (closed)

sohstationviewer/view/main_window.py

@@ -720,6 +720,7 @@ class MainWindow(QtWidgets.QMainWindow, UIMainWindow):
         """
         if self.has_problem:
             return
+        self.clear_plots()
         self.is_plotting_soh = True
 
         d_obj = self.data_object