Only remove last Laue spot when back pressed

This was previously removing all Laue spots in the current detector
when the back button was pressed. Only remove the last Laue spot.

Signed-off-by: Patrick Avery <[email protected]>

Author: psavery

hexrd/ui/calibration/calibration_runner.py

@@ -420,4 +420,5 @@ def last_point_removed(self):
             self.current_data_list.pop(-1)
         elif self.active_overlay_type == OverlayType.laue:
             self.decrement_overlay_data_index()
-            self.current_data_list.clear()
+            if self.current_data_list:
+                self.current_data_list.pop(-1)