fix(router-store): set undefined for unserializable route title

[markostanimirovic]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Closes #3495

What is the new behavior?

MinimalRouterStateSerializer sets undefined for unserializable route title.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

This is a temporary fix to avoid runtime errors when the @ngrx/router-store package is used with a custom title resolver in Angular 14. I'll create another PR that completely resolves this issue when we move to Angular 15 (that includes this fix angular/angular#47459).

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