fix(gitlab): catch/throw ‘empty’ error

lib/platform/gitlab/index.js

@@ -160,6 +160,9 @@ async function initRepo({
     await Promise.all([getPrList(), getFileList()]);
   } catch (err) /* istanbul ignore next */ {
     logger.debug('Caught initRepo error');
+    if (err.message.includes('HEAD is not a symbolic ref')) {
+      throw new Error('empty');
+    }
     if (err.message === 'archived') {
       throw err;
     }