fix(docker): throw error if no manifest config

lib/datasource/docker/index.js

@@ -382,6 +382,11 @@ async function getLabels(registry, repository, tag) {
     const manifest = JSON.parse(manifestResponse.body);
     let labels = {};
     const configDigest = manifest.config.digest;
+    // istanbul ignore if
+    if (!manifest.config) {
+      logger.warn({ manifest }, 'Docker manifest error: no config');
+      throw new Error('registry-failure');
+    }
     const headers = await getAuthHeaders(registry, repository);
     if (!headers) {
       logger.info('No docker auth found - returning');