PEP 622: Fix Django example (#1523)

Closes gvanrossum/patma#135

Author: brandtbucher

pep-0622.rst

@@ -188,7 +188,7 @@ sequence. With the proposal in this PEP, we could rewrite that code
 into this::
 
     match value:
-        case [*v, label := (Promise() | str())]:
+        case [*v, label := (Promise() | str())] if v:
             value = tuple(v)
         case _:
             label = key.replace('_', ' ').title()