Fix spurious generation of empty 'Alternative Name' in place.merge()

with an empty name

Bug discovered during testing of fix to 8233 (thanks, Enno for
discovering the problem and the fix).

gramps/gen/lib/place.py

@@ -570,7 +570,7 @@ class Place(CitationBase, NoteBase, MediaBase, UrlBase, PrimaryObject):
         :param acquisition: instance to merge
         :type acquisition: :class:'~.place.Place
         """
-        if acquisition.name not in self.alt_names:
+        if acquisition.name and (acquisition.name not in self.alt_names):
             self.alt_names.append(acquisition.name)
 
         for addendum in acquisition.alt_names: