qapi: Tweak "command returns a nice type" check for clarity

Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Message-Id: <20191120182551.23795-2-armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>

scripts/qapi/schema.py

@@ -711,10 +711,11 @@ class QAPISchemaCommand(QAPISchemaEntity):
             self.ret_type = schema.resolve_type(
                 self._ret_type_name, self.info, "command's 'returns'")
             if self.name not in self.info.pragma.returns_whitelist:
-                if not (isinstance(self.ret_type, QAPISchemaObjectType)
-                        or (isinstance(self.ret_type, QAPISchemaArrayType)
-                            and isinstance(self.ret_type.element_type,
-                                           QAPISchemaObjectType))):
+                typ = self.ret_type
+                if isinstance(typ, QAPISchemaArrayType):
+                    typ = self.ret_type.element_type
+                    assert typ
+                if not isinstance(typ, QAPISchemaObjectType):
                     raise QAPISemError(
                         self.info,
                         "command's 'returns' cannot take %s"