Handle S3 errors without a statusCode (#700)

If an error occurs with the SDK before an HTTP request is made then the error's statusCode will be `undefined`, which will trigger a TypeError in common code outside the plugin. 

This change sets a fallback 500 status code so that error handling can continue.

plugins/aws-s3-storage/src/s3Errors.ts

@@ -44,6 +44,6 @@ export function convertS3Error(err: AWSError): VerdaccioError {
       return getInternalError('request aborted');
     default:
       // @ts-ignore
-      return getCode(err.statusCode, err.message);
+      return getCode(err.statusCode || HTTP_STATUS.INTERNAL_ERROR, err.message);
   }
 }