Fix nil-pointer on accessing condition in autoscaler

[markusthoemmes]

Proposed Changes

Seen in the wild as

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x60 pc=0x17b7be5]

goroutine 156 [running]:
knative.dev/serving/pkg/reconciler/autoscaling/kpa.(*Reconciler).ReconcileKind(0xc00066d6b0, 0x2030d40, 0xc001767c50, 0xc0017026c0, 0x1ff71a0, 0xc001702878)
	/go/src/knative.dev/serving/pkg/reconciler/autoscaling/kpa/kpa.go:151 +0x1335
knative.dev/serving/pkg/client/injection/reconciler/autoscaling/v1alpha1/podautoscaler.(*reconcilerImpl).Reconcile(0xc0003f5130, 0x2030d40, 0xc001767bc0, 0xc0024d6150, 0x21, 0xc001686db0, 0x2030d40)
	/go/src/knative.dev/serving/pkg/client/injection/reconciler/autoscaling/v1alpha1/podautoscaler/reconciler.go:253 +0x146c
knative.dev/pkg/controller.(*Impl).processNextWorkItem(0xc0006b01c0, 0x0)
	/go/src/knative.dev/serving/vendor/knative.dev/pkg/controller/controller.go:511 +0x728
knative.dev/pkg/controller.(*Impl).RunContext.func3(0xc0016e1860, 0xc0006b01c0)
	/go/src/knative.dev/serving/vendor/knative.dev/pkg/controller/controller.go:449 +0x53
created by knative.dev/pkg/controller.(*Impl).RunContext
	/go/src/knative.dev/serving/vendor/knative.dev/pkg/controller/controller.go:447 +0x1f5

Release Note

Fixed a rare nil-pointer exception in the autoscaler

/assign @julz @vagababov

[julz]

/lgtm

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: julz, markusthoemmes

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• pkg/reconciler/autoscaling/OWNERS [julz,markusthoemmes]

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[codecov]

Codecov Report

Merging #9794 into master will decrease coverage by 0.02%.
The diff coverage is 63.95%.

@@            Coverage Diff             @@
##           master    #9794      +/-   ##
==========================================
- Coverage   87.77%   87.74%   -0.03%     
==========================================
  Files         180      180              
  Lines        8499     8553      +54     
==========================================
+ Hits         7460     7505      +45     
- Misses        791      798       +7     
- Partials      248      250       +2     

Impacted Files	Coverage Δ
cmd/activator/main.go	0.00% <0.00%> (ø)
cmd/autoscaler/main.go	13.13% <0.00%> (-0.14%)	⬇️
pkg/queue/health/probe.go	93.93% <ø> (ø)
cmd/queue/main.go	0.51% <50.00%> (+0.51%)	⬆️
...g/apis/serving/v1alpha1/domainmapping_lifecycle.go	70.58% <64.28%> (+3.92%)	⬆️
pkg/apis/serving/v1/revision_validation.go	80.00% <66.66%> (+2.22%)	⬆️
pkg/reconciler/domainmapping/reconciler.go	85.00% <66.66%> (+13.12%)	⬆️
pkg/autoscaler/statforwarder/forwarder.go	81.18% <68.18%> (-3.12%)	⬇️
pkg/activator/net/lb_policy.go	91.17% <100.00%> (ø)
pkg/apis/serving/v1/configuration_validation.go	100.00% <100.00%> (ø)
... and 7 more

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