Fix bug happen when user stop the process before data object is created

closes #143 (closed)

add try except to by pass checking data_object's keys when stopping before data_object is created

sohstationviewer/view/main_window.py

@@ -893,8 +893,11 @@ class MainWindow(QtWidgets.QMainWindow, UIMainWindow):
         self.is_plotting_waveform = False
         self.is_plotting_tps = False
         self.is_stopping = False
-        if len(self.data_object.keys) > 1:
-            self.plot_diff_key_button.setEnabled(True)
+        try:
+            if len(self.data_object.keys) > 1:
+                self.plot_diff_key_button.setEnabled(True)
+        except AttributeError:
+            pass
 
     @QtCore.Slot()
     def reset_is_plotting_waveform(self):