pkg/chunkenc: fix leak of pool.

[johncming]

There is a situation than some items from the pool can't put back to the pool when return after error.

[CLAassistant]

All committers have signed the CLA.

[pstibrany]

I believe that's intentional. They are not leaked, but will be garbage collected.

[johncming]

I believe that's intentional. They are not leaked, but will be garbage collected.

Yes, the unused objects are always gc-ed. But using pool here is for alleviating many tiny allocations.

[cyriltovena]

LGTM I don't think this is going to make a huge difference as this is never really happening.

But for the sake of doing it cleanly, let's go !