ModerationInformation::isLatestRevision() is naive, fails fatally (Call to a member function getRevisionId() on null)

ModerationInformation::isLatestRevision() unconditionally calls isLatestRevision() on ModerationInformation::getLatestRevision(), but ModerationInformation::getLatestRevision() can return NULL, which causes a fatal error. This is precisely what happens on the node/{nid}/latest path if you have node access in place. Here are steps to reproduce:

1. Install Drupal using the Standard install profile.
2. Install workbench_moderation.
3. Create a user role with permission create Articles and permission to perform all the default state transitions.
4. Create a user with that role.
5. Log out and back into the site as the new user. (User 1 bypasses all access checks and thus won't see the bug.)
6. Create an article and save it in the Draft state.
7. You should be redirected to node/1/latest, and it should display just fine.
8. Install any node access module. I used view_unpublished. (Don't rebuild the node access permissions yet.)
9. Reload node/1/latest, and it should display just fine.
10. Rebuild node access permissions and reload node/1/latest.
11. Bug: You will get an error like this:
    

    Fatal error: Call to a member function getRevisionId() on null in /var/www/d8/modules/contrib/workbench_moderation/src/ModerationInformation.php on line 177