Soul lanterns floating in ancient cities

When generating an ancient city, soul lanterns don't necessarily need to have a block underneath them if they already have a block above them. This wouldn't be a problem, except for the possibility of

Steps to reproduce the issue:

1. Go to seed 0.

2. Go to coordinates 21678 -41 1248.

3. Look at the soul lantern, and notice that it is not connected to the block above.

Expected result:

The soul lantern should not be generated, it should be connected to the ceiling or the block below the lantern should not be replaced with air.

Actual result:

The soul lantern appears disconnected from the ceiling.