Soul Lanterns can generate floating in ancient cities

The Bug:

Soul Lanterns can generate floating in ancient cities.

Steps to Reproduce:

1. Create a world with this seed: 111111111111111111
2. Go to this position: -416 -44 -753

Expected Results:

Soul Lanterns should not generate without a supporting block in ancient cities.

Observed Results:

Soul Lanterns can generate floating in ancient cities.