Chunks that were corrupted before 1.18 are missing anything below y 0

When an old world (like from windows 10 beta 0.15>) was loaded before the cave updates, these chunks are removed. But if these chunks are updated, the blocks below y=0 are still missing. This shouldn't happen and instead generate the caves below y=0.

 

Steps to Reproduce:

1. Take any old world created and last loaded before 0.15.0

2. If the world is loaded in a newer version like 1.16 before the cave update, the alpha chunks will be deleted.

3. Load world in newer/newest version after 1.18

 

Observed Results:

After updating the world, there are no blocks generated below y=0 from the caves and cliffs update.

 

Expected Results:

There should be new blocks generated below y=0 from the caves update in the missing chunk.

 

Note: The Chunks that aren't voided weren't loaded in alpha. These were generated in 1.16 or 1.20.