[#3512157] Added better access check on local task links.

[richardgaunt]

Checklist before requesting a review

• I have formatted the subject to include ticket number as Issue #123456 by drupal_org_username: Issue title
• I have added a link to the issue tracker
• I have provided information in Changed section about WHY something was done if this was not a normal implementation
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• I have run new and existing relevant tests locally with my changes, and they passed
• I have provided screenshots, where applicable

Changed

1. Added check for boolean access value rather than just expecting an AccessInterface object
2. Added better check of link array properties in local tasks preprocessing.