Worlds saved in the spectator cause to crash when loading the world

Summary:
Worlds saved in the spectator cause to crash when loading the world. This also applies to worlds created and saved in other versions.

Steps to reproduce:

1. Create a new world with cheats enabled.

2. Switch to spectator.

3. Save the world.

4. Try to enter this world.

Observed results:
Minecraft crashes when loading the world.

Expected results:
Worlds shouldn't crash.

World example: