fail validation if validate returns False

ExtensionPoint.validate returns False when any error is raised

ListServerExtension does not check the return value, only errors

Author: minrk

jupyter_server/extension/serverextension.py

@@ -306,7 +306,8 @@ def list_server_extensions(self):
                                 GREEN_ENABLED if enabled else RED_DISABLED))
                 try:
                     self.log.info("    - Validating {}...".format(name))
-                    extension.validate()
+                    if not extension.validate():
+                        raise ValueError("validation failed")
                     version = extension.version
                     self.log.info(
                         "      {} {} {}".format(name, version, GREEN_OK)