Fix NPE for gRPC empty stream

[EveryAndrey]

Context

When for gRPC stream Response wasn't called onNext() before onComplete() (that is a valid case) then we got NPE at row
'requireNonNull(responseAttachmentBuilder).setStatus(status.toString());' because it expects only single or multiple response values.

Checklist

• Sign Allure CLA
• Provide unit tests

[dtuchs]

@baev @EveryAndrey it is fixed in #1015
Methods private <T, A> GrpcRequestAttachment.Builder requestAttachment(final MethodDescriptor<T, A> method)
and
private <T, A> GrpcResponseAttachment.Builder responseAttachment(final MethodDescriptor<T, A> method, final io.grpc.Status status, final Metadata metadata)
just return empty array attachement ( []) for epmty streams.