[#327] rpc: Fix mem leak

gRPC stream must be closed by `cancel` to prevent memleak.

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

api/rpc/client/flows.go

@@ -109,7 +109,9 @@ func (s *serverStreamReaderCloser) ReadMessage(msg message.Message) error {
 
 	err = s.rw.ReadMessage(msg)
 	if !errors.Is(err, io.EOF) {
-		s.rw.cancel()
+		if err != nil {
+			s.rw.cancel()
+		}
 		return err
 	}