Nether Portal able to replace unbreakable blocks, allowing access to void

Nether portals due to the way they spawn can destroy bedrock when a new portal spawns. Only happens in certain criterias, but is possible to recreate. This is private due to it exposing a game breaking bug! First discovered in a Forge Dev 1.7.10 Environment.

What happened: Portal destroys bedrock instead of being placed above it

Expected: Portal to, if it can't find some block that isn't bedrock, to be 1 block above or act like the nether portal tries to generate above fluid and goto about Y = 70.

To reproduce:
1. Clean out a huge hole, either by making a bedrock superflat, or blowing it up
2. Go to the nether
3. Go to the coordinates of the hole / 8(because nether travel.)
4. Go to the overworld
5. See that it replaced the bedrock.

Video on how to reproduce: https://youtu.be/UzBwtM2813c

Affects:

• bedrock
• end portal
• end portal frames
• barriers
• command blocks
• structure blocks