Support checking if obj is a nil ptr

[zhifei92]

What type of PR is this?
/kind feature

What this PR does / why we need it:
IsNilPtr checks if the provided object is a nil pointer. This is specially useful when dealing with interfaces that may hold pointers.

Relevant issues: kubernetes/kubernetes#125561

the nil checking for interface RuntimeHandlerResolver in #L109 will never check whether the underlying struct is nil.
A reflect nil checking is needed to avoid panic in running 'rcManager.LookupRuntimeHandler'(#L111)

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Release note:

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: zhifei92
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[k8s-ci-robot]

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[googs1025]

Is this method called from anywhere other than testing?

[zhifei92]

yes

[k8s-triage-robot]

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/lifecycle stale

[k8s-triage-robot]

The Kubernetes project currently lacks enough active contributors to adequately respond to all PRs.

This bot triages PRs according to the following rules:

• After 90d of inactivity, lifecycle/stale is applied
• After 30d of inactivity since lifecycle/stale was applied, lifecycle/rotten is applied
• After 30d of inactivity since lifecycle/rotten was applied, the PR is closed

You can:

• Mark this PR as fresh with /remove-lifecycle rotten
• Close this PR with /close
• Offer to help out with Issue Triage

Please send feedback to sig-contributor-experience at kubernetes/community.

/lifecycle rotten