Flying under bedrock level in spectator mode at max speed causes FPS drop

Steps to Reproduce:
1. Go into /gamemode 3 and press F3 to see the FPS.
2. Increase the flight speed to maximum. (it is not as noticeable at lower speeds).
3. Fly below the bedrock level for a few seconds.

Observed Result:

• The game will stutter just before hitting bedrock level, and below bedrock, there's a noticeable FPS drop.

Expected Result:

• The game should still run smoothly.