Igloo sometimes generates with "basement" passage through bedrock

Summary:
Igloo sometimes generates with "basement" passage through bedrock.

Steps to reproduce:

1. Create a world with seed -3453372036209748871
2. Teleport to coordinates /tp 723 -63 -755
3. Break the floor block below you.

Observed results:
The igloo replaces the bedrock.

Expected results:
Igloo will not replace bedrock when generating.