Fix Locations Gramplet (Enclosed by) to properly displaycertain nested places. (#1127)

when the smallest place has undated enclosure and larger places are dated.

Issue #11691

gramps/plugins/gramplet/locations.py

@@ -300,6 +300,8 @@ class DateRange:
         """
         start = None
         stop = None
+        if date.is_empty():
+            return (None, None)
         if date.modifier == Date.MOD_NONE:
             start = date.sortval
             stop = date.sortval