Issue Description: creating an elevator with bedrock will delete the bedrock

What happens: if the elevator is created with a normal block and a bedrock peace it will delete the bedrock (i.e. selecting bedrock then a usable block)

What you expected to happen: it should either not create the elevator if bedrock is detected or ignore that section of the selected area.

Steps to reproduce:

1. Use the linking tool to select your first point.
2. select the next one either on the same level including bedrock or at Y=0 if the first one on a usable block
3. once it attempts to create the elevator it deletes any block that was not usable being bedrock.

Affected Versions (Do not use "latest"): Replace with a list of all mods you have in.

• Thutcore: using AIO 1.11.2 embedded version
• Minecraft: 1.12.2
• Forge: 14.23.5.2768
• thuttech: 6.1.5