fix sdNotify func when debug level

[calvin0327]

When I was debugging locally with flag --log-level=debug, I saw the following log message：

so, if the err is nil, we should not to print the message.

[k8s-ci-robot]

Hi @calvin0327. Thanks for your PR.

I'm waiting for a containerd member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[fuweid]

would you use real name in the signoff ? Thanks

[calvin0327]

would you use real name in the signoff ? Thanks

that's sure. updated