Tweak the message for variants

Although the code does not, in fact, know about them, it's more
pertinent to say that they're unsupported than to say that the variant
in question is unknown.

Change-Id: I411d792dc91f2d7af58a4b7919c952a005b3417e
Reviewed-by: Cristian Maureira-Fredes <cristian.maureira-fredes@qt.io>

util/locale_database/cldr.py

@@ -352,7 +352,11 @@ class CldrAccess (object):
                 parts.append(text)
         if len(parts) > 1:
             parts[-1] = 'and ' + parts[-1]
-        assert parts
+        else:
+            assert parts
+            if parts[0].startswith('variant'):
+                raise Error(f'No support for {parts[0]}',
+                            language, script, territory, variant)
         raise Error('Unknown ' + ', '.join(parts),
                     language, script, territory, variant)