grpc client error fix (#1351)

Co-authored-by: Ben Toogood <ben@micro.mu>

grpc.go

@@ -445,6 +445,10 @@ func (g *grpcClient) Call(ctx context.Context, req client.Request, rsp interface
 		// call backoff first. Someone may want an initial start delay
 		t, err := callOpts.Backoff(ctx, req, i)
 		if err != nil {
+			if verr, ok := err.(*errors.Error); ok {
+				return verr
+			}
+
 			return errors.InternalServerError("go.micro.client", err.Error())
 		}