In spectator mode, the player can disable flight mode

Summary:
In spectator mode, the player can disable flight mode. This results in the player not being able to change height.

Steps to reproduce:

1. Switch to spectator mode (/gamemode 6).
2. Turn off the flight mode (by pressing the jump button twice).
3. Try moving up and down (height).

Observed results:
The player cannot change altitude when flying mode is disabled.

Expected results:
The player will not be able to disable the flight mode to be able to move in height.