[#1662] object: Fix CloseAndRecv for patch streamer

* A client may open stream to server, not send anything and close
  the open stream immediatly. This shouldn't cause a panic;
* Return the error if `s.patcher` is uninitialized. Uninitialized
  patcher cannot be closed, this causes a panic.

Signed-off-by: Airat Arifullin <a.arifullin@yadro.com>

pkg/services/object/patch/streamer.go

@@ -214,6 +214,9 @@ func (s *Streamer) Send(ctx context.Context, req *objectV2.PatchRequest) error {
 }
 
 func (s *Streamer) CloseAndRecv(ctx context.Context) (*objectV2.PatchResponse, error) {
+	if s.patcher == nil {
+		return nil, errors.New("uninitialized patch streamer")
+	}
 	patcherResp, err := s.patcher.Close(ctx)
 	if err != nil {
 		return nil, err