Wart blocks still generate in places where the nylium floor is missing

Extracted from MC-187355.

At some places in the nether, the nylium floor is missing (see MC-187355). However, the wart blocks in the floor still generate at these locations.

To reproduce

Seed: 8933751030273973285
/execute in minecraft:the_nether run tp @s -517.68 82.56 86.57 640.45 65.25