Slowing or increasing ticking affects time calculation in demo mode

Slowing or increasing ticking affects time calculation in demo mode

Steps to Reproduce:

1. Switch the version to "Latest Snapshot" on an account that owns the game
   This step won't be necessary once the /tick command gets into a full release
2. Open the demo world to LAN with cheats enabled
3. Use the /tick command (ie: /tick freeze)
4. Time is frozen

Observed Results:
Minecraft demo time calculation frozen

 

Expected Results:

Don't freeze the game time calculation in Demo