Incorrect Backup CR config for CSI backup causes backup to fail due to runtime error

[shubham-pampattiwar]

What steps did you take and what happened:
When we try to use Velero backup for CSI volumes via incorrect Backup CR config, the backup fails due to nil pointer dereference and velero pod restarts. For example:

apiVersion: velero.io/v1
kind: Backup
metadata:
  name: cluster-pvcs
  namespace: openshift-adp
spec:
  csiSnapshotTimeout: 10m0s
  defaultVolumesToRestic: false
  includedNamespaces:
    - '*'
  includedResources:
    - PersistentVolumeClaim
  labelSelector:
    matchLabels:
      oadp-backup: 'true'
  storageLocation: openshift-backups-1
  ttl: 24h0m0s

This backup CR will cause incomplete execution of the velero-plugin-for-csi as the includedResources only consists of PVC and thus excluded VolumeSnapshots, VolumeSnapshotContents etc.

Error logs in velero pod as velero tries to delete resources that do not exist:

2022/09/15 02:23:35  info Waiting for CSI driver to reconcile volumesnapshot mssql-persistent/velero-mssql-pvc-f7x6j. Retrying in 5s
2022/09/15 02:23:40  info Waiting for CSI driver to reconcile volumesnapshot mssql-persistent/velero-mssql-pvc-f7x6j. Retrying in 5s
2022/09/15 02:23:45  info Waiting for CSI driver to reconcile volumesnapshot mssql-persistent/velero-mssql-pvc-f7x6j. Retrying in 5s
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x1a8b3cd]

goroutine 2372 [running]:
github.com/vmware-tanzu/velero/pkg/controller.(*backupController).deleteVolumeSnapshot.func1(0xc000d5e140)
        /remote-source/src/github.com/vmware-tanzu/velero/pkg/controller/backup_controller.go:949 +0xad
created by github.com/vmware-tanzu/velero/pkg/controller.(*backupController).deleteVolumeSnapshot
        /remote-source/src/github.com/vmware-tanzu/velero/pkg/controller/backup_controller.go:945 +0xf7

What did you expect to happen:
Backup to complete successfully

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