Ensure anonymous user always exists in the system

Problem/Motivation

In professional secure environments data obfuscation or truncation is a must, to ensure that PII (personal identifiable information) is not present on developers machines. Such solutions may include truncation of all users data (i.e. when database backup is being exported without user tables). This leads to missing anonymous user in Drupal resulting in random errors on Drupal side.

Steps to reproduce

- Truncate users table
- Try to use the site as usual. You'll likely experience a random error.

Proposed resolution

Ensure that anonymous user always exists and create it if not.