Don't attempt to call set_orientation if self.pui is None

pui can be None if a gramplet fails to load.

Fixes #13820

Author: stevenyoungs

gramps/gui/widgets/grampletbar.py

@@ -680,7 +680,8 @@ def set_orientation(self, orientation):
         """
         Called when the gramplet orientation changes.
         """
-        self.pui.set_orientation(orientation)
+        if self.pui:
+            self.pui.set_orientation(orientation)
 
 
 # -------------------------------------------------------------------------