[fix][meta] Fix NPE in shouldIgnoreEvent when MetadataEvent options is null

[SongOf]

Motivation

AbstractMetadataStore#shouldIgnoreEvent normalizes a possibly-null
MetadataEvent#getOptions() into a local options variable
(options = event.getOptions() != null ? event.getOptions() : Collections.emptySet()),
but the ephemeral/sequential check on the next lines only used it for the first half of
the condition:

if (options.contains(CreateOption.Ephemeral) || event.getOptions().contains(CreateOption.Sequential)) {

When a synchronizer delivers a MetadataEvent whose options is null and the metadata
is not Ephemeral, the short-circuit falls through to
event.getOptions().contains(...) and throws a NullPointerException, so the event
fails to be processed instead of being handled by the remaining checks.

Modifications

Use the null-normalized local options variable for the CreateOption.Sequential
check as well, matching the CreateOption.Ephemeral check on the same line. No
behavior change other than removing the NPE path.

Verifying this change

- [x] Make sure that the change passes the CI checks.

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

- [ ] Dependencies (add or upgrade a dependency)
- [ ] The public API
- [ ] The schema
- [ ] The default values of configurations
- [ ] The threading model
- [ ] The binary protocol
- [ ] The REST endpoints
- [ ] The admin CLI options
- [ ] The metrics
- [ ] Anything that affects deployment

[void-ptr974]

LGTM.