client: fix goroutine leak in unreleased context

If headerTimeout is not zero then two context are created but only one is released.
cancelCtx in this case is never released which leads to goroutine leak inside it.

client/client.go

@@ -378,9 +378,12 @@ func (c *simpleHTTPClient) Do(ctx context.Context, act httpAction) (*http.Respon
 		return nil, nil, err
 	}
 
-	hctx, hcancel := context.WithCancel(ctx)
+	var hctx context.Context
+	var hcancel context.CancelFunc
 	if c.headerTimeout > 0 {
 		hctx, hcancel = context.WithTimeout(ctx, c.headerTimeout)
+	} else {
+		hctx, hcancel = context.WithCancel(ctx)
 	}
 	defer hcancel()