When a job entry is absent from scheduler.yaml status map, the PHP
runtime correctly treats it as enabled, but the Twig template was
incorrectly showing it as disabled due to Twig's `null is defined`
evaluating to true. Simplified the check to only disable when
explicitly set to 'disabled'.
Fixesgetgrav/grav#4047
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>