fix ejob nil pointer bug

[hellolijj]

Ⅰ. Describe what this PR does

fix ejob nil pointer.

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how to verify it

ejob controller will not panic if ejob.spec.replicas not set.

E0706 15:49:38.652110 655 runtime.go:78] Observed a panic: "invalid memory address or nil pointer dereference" (runtime error: invalid memory address or nil pointer dereference) goroutine 1837 [running]: k8s.io/apimachinery/pkg/util/runtime.logPanic({0x1a206c0, 0x2e57b80}) /home/admin/204_20220705195047156_295115616_code/kruise/vendor/k8s.io/apimachinery/pkg/util/runtime/runtime.go:74 +0x85 k8s.io/apimachinery/pkg/util/runtime.HandleCrash({0x0, 0x0, 0xc0262d7fe0}) /home/admin/204_20220705195047156_295115616_code/kruise/vendor/k8s.io/apimachinery/pkg/util/runtime/runtime.go:48 +0x75 panic({0x1a206c0, 0x2e57b80}) /usr/local/go/src/runtime/panic.go:1038 +0x215 github.com/openkruise/kruise/pkg/controller/ephemeraljob.(*ReconcileEphemeralJob).filterPods(0xc0160c2e40, 0xc01f1e5880) /home/admin/204_20220705195047156_295115616_code/kruise/pkg/controller/ephemeraljob/ephemeraljob_controller.go:258 +0x31e

Ⅳ. Special notes for reviews

[codecov-commenter]

Codecov Report

Merging #1016 (dcad401) into master (5380c57) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1016      +/-   ##
==========================================
+ Coverage   49.64%   49.66%   +0.01%     
==========================================
  Files         124      124              
  Lines       12078    12078              
==========================================
+ Hits         5996     5998       +2     
+ Misses       5166     5164       -2     
  Partials      916      916              

Flag	Coverage Δ
unittests	49.66% <ø> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/controller/daemonset/daemonset_update.go	55.75% <0.00%> (+0.88%)	⬆️

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[sonatype-lift]

gofmt: File is not gofmt-ed with -s

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Was this a good recommendation?
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[FillZpp]

/lgtm

[kruise-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: FillZpp

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