Client.Call(): do not return error if no Status is set (gRPC v1.23 and up)

To account for 5da5b1f225,
which is part of gRPC v1.23.0 and up, and after which gRPC no longer sets a
Status if no error occured.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

client.go

@@ -134,11 +134,11 @@ func (c *Client) Call(ctx context.Context, service, method string, req, resp int
 		return err
 	}
 
-	if cresp.Status == nil {
-		return errors.New("no status provided on response")
+	if cresp.Status != nil {
+		return status.ErrorProto(cresp.Status)
 	}
 
-	return status.ErrorProto(cresp.Status)
+	return nil
 }
 
 func (c *Client) dispatch(ctx context.Context, req *Request, resp *Response) error {