🐛 capd: fix nil pointer in dockermachinepool controller

[chrischdi]

What this PR does / why we need it:

Fixes nil pointer which occurred e.g. here:

• https://prow.k8s.io/view/gs/kubernetes-jenkins/logs/periodic-cluster-api-e2e-mink8s-main/1812401250918993920
• CAPD logs: https://storage.googleapis.com/kubernetes-jenkins/logs/periodic-cluster-api-e2e-mink8s-main/1812401250918993920/artifacts/clusters/bootstrap/logs/capd-system/capd-controller-manager/capd-controller-manager-64d8bd4d45-77kh8/manager.log

{"ts":1720949295165.3877,"caller":"controller/controller.go:110","msg":"Observed a panic in reconciler: assignment to entry in nil map","controller":"dockermachinepool","controllerGroup":"infrastructure.cluster.x-k8s.io","controllerKind":"DockerMachinePool","DockerMachinePool":{"name":"autoscaler-qynhbr-mp-0-4hrqc","namespace":"autoscaler-wh9wa3"},"namespace":"autoscaler-wh9wa3","name":"autoscaler-qynhbr-mp-0-4hrqc","reconcileID":"5982a440-3d63-4817-b8fa-549b825f7753","v":0}
panic: assignment to entry in nil map [recovered]
	panic: assignment to entry in nil map

goroutine 325 [running]:
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Reconcile.func1()
	sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:111 +0x1e5
panic({0x1d48ca0?, 0x2370970?})
	runtime/panic.go:770 +0x132
sigs.k8s.io/cluster-api/test/infrastructure/docker/exp/internal/controllers.(*DockerMachinePoolReconciler).propagateMachineDeleteAnnotation(0xc0004fa8c0, {0x23955e0, 0xc00062fb00}, 0xc000fd8290)
	sigs.k8s.io/cluster-api/test/infrastructure/docker/exp/internal/controllers/dockermachinepool_controller_phases.go:326 +0x253
sigs.k8s.io/cluster-api/test/infrastructure/docker/exp/internal/controllers.(*DockerMachinePoolReconciler).reconcileDockerMachines(0xc0004fa8c0, {0x23955e0, 0xc00062fb00}, 0xc0012041a0, 0xc000418848, 0xc001716c40)
	sigs.k8s.io/cluster-api/test/infrastructure/docker/exp/internal/controllers/dockermachinepool_controller_phases.go:190 +0x112c
sigs.k8s.io/cluster-api/test/infrastructure/docker/exp/internal/controllers.(*DockerMachinePoolReconciler).reconcileNormal(0xc0004fa8c0, {0x23955e0, 0xc00062fb00}, 0xc0012041a0, 0xc000418848, 0xc001716c40)
	sigs.k8s.io/cluster-api/test/infrastructure/docker/exp/internal/controllers/dockermachinepool_controller.go:288 +0x13e
sigs.k8s.io/cluster-api/test/infrastructure/docker/exp/internal/controllers.(*DockerMachinePoolReconciler).Reconcile(0xc0004fa8c0, {0x23955e0, 0xc00062f6e0}, {{{0xc0010b1410?, 0x3?}, {0xc0000585c0?, 0xc000accd10?}}})
	sigs.k8s.io/cluster-api/test/infrastructure/docker/exp/internal/controllers/dockermachinepool_controller.go:157 +0x8b0
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Reconcile(0x239c460?, {0x23955e0?, 0xc00062f6e0?}, {{{0xc0010b1410?, 0xb?}, {0xc0000585c0?, 0x0?}}})
	sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:114 +0xb7
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).reconcileHandler(0xc000330840, {0x2395618, 0xc0004df950}, {0x1e0ab60, 0xc001935920})
	sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:311 +0x3bc
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem(0xc000330840, {0x2395618, 0xc0004df950})
	sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:261 +0x1be
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2.2()
	sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:222 +0x79
created by sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2 in goroutine 102
	sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:218 +0x486

triage link

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

/area provider/infrastructure-docker

[chrischdi]

/cherry-pick release-1.7
/cherry-pick release-1.6

[k8s-infra-cherrypick-robot]

@chrischdi: once the present PR merges, I will cherry-pick it on top of release-1.7 in a new PR and assign it to you.

In response to this:

/cherry-pick release-1.7
/cherry-pick release-1.6

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[chrischdi]

/cherry-pick release-1.6

[k8s-infra-cherrypick-robot]

@chrischdi: once the present PR merges, I will cherry-pick it on top of release-1.6 in a new PR and assign it to you.

In response to this:

/cherry-pick release-1.6

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[sbueringer]

Thx!

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 634832ef6359ebd07dd24c747886fe5518b290f7

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sbueringer

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[k8s-infra-cherrypick-robot]

@chrischdi: new pull request created: #10877

In response to this:

/cherry-pick release-1.7
/cherry-pick release-1.6

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[k8s-infra-cherrypick-robot]

@chrischdi: new pull request created: #10878

In response to this:

/cherry-pick release-1.6

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