generate kustomize manifests: skip parsing definitions on a non-existent API root dir

[estroz]

Description of the change:

• internal/generate/clusterserviceversion/bases/definitions: skip on a non-existent API root dir

Motivation for the change: bugfix

/kind bug

Checklist

If the pull request includes user-facing changes, extra documentation is required:

• Add a new changelog fragment in changelog/fragments (see changelog/fragments/00-template.yaml)
• Add or update relevant sections of the docs website in website/content/en/docs

[estroz]

/cherry-pick v1.4.x

[openshift-cherrypick-robot]

@estroz: cannot checkout v1.4.3: error checking out v1.4.3: exit status 1. output: error: pathspec 'v1.4.3' did not match any file(s) known to git

In response to this:

/cherry-pick v1.4.3

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/test-infra repository.

[openshift-cherrypick-robot]

@estroz: cannot checkout v1.4.3: error checking out v1.4.3: exit status 1. output: error: pathspec 'v1.4.3' did not match any file(s) known to git

In response to this:

/cherry-pick v1.4.3

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/test-infra repository.

[openshift-cherrypick-robot]

@estroz: new pull request created: #4625

In response to this:

/cherry-pick v1.4.x

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/test-infra repository.