setup: catch and don't stop on any exception in fetching the legacy plugins.

rhodecode/authentication/__init__.py

@@ -71,9 +71,12 b' def _discover_legacy_plugins(config, pre'
     setting in database which are using the specified prefix. Normally 'py:' is
     used for the legacy plugins.
     """
+    try:
     auth_plugins = SettingsModel().get_setting_by_name('auth_plugins')
     enabled_plugins = auth_plugins.app_settings_value
     legacy_plugins = [id_ for id_ in enabled_plugins if id_.startswith(prefix)]
+    except Exception:
+        legacy_plugins = []
 
     for plugin_id in legacy_plugins:
         log.debug('Legacy plugin discovered: "%s"', plugin_id)