client: consistently use defer for ensureReaderClosed

ensureReaderClosed was designed to be usable regardless if a response
was nil (error) or non-nil (success). Some code-paths were optimized to
avoid using a defer (which used to have an overhead), but the overhead
of defer is neglectable in current versions of Go, and some of these
optimizations made the logic more complicated (and err-prone).

This patch switches to use a defer for all places.

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

client/swarm_unlock.go

@@ -9,6 +9,6 @@ import (
 // SwarmUnlock unlocks locked swarm.
 func (cli *Client) SwarmUnlock(ctx context.Context, req swarm.UnlockRequest) error {
 	resp, err := cli.post(ctx, "/swarm/unlock", nil, req, nil)
-	ensureReaderClosed(resp)
+	defer ensureReaderClosed(resp)
 	return err
 }