🐛 Do not set PatchType if patch is empty

[tatsuhiro-t]

In admission v1, API server requires that Patch and PatchType are both
provided or none are provided. Meanwhile, admission v1beta1 does not
have this kind of requirement.

In controller-runtime, PatchResponseFromRaw sets PatchType regardless
of the existence of patch. If patch is empty, a response contains
only PatchType and API server does not like it. Webhook call fails.

This change fixes this issue by not setting PatchType if patch is
empty.

Fixes #1295

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[tatsuhiro-t]

/assign @gerred

[alvaroaleman]

/lgtm
/approve

Thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: alvaroaleman, tatsuhiro-t

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