Automatic merge from submit-queue (batch tested with PRs 48231, 47377, 48797, 49020, 49033)

prevent unsetting of nonexistent previous port in kubeapi-load-balancer charm

**What this PR does / why we need it**: prevent unsetting of nonexistent previous port in kubeapi-load-balancer charm

**Release note**:
```release-note
prevent unsetting of nonexistent previous port in kubeapi-load-balancer charm
```