When I built a portal to the Nether, the Nether began to generate and then the game crashed. When I opened the world again, there was no portal in the nether to return to the overworld with.

Steps to reproduce:

1. I'm unsure if this is important, but my seed was -3852560259466459530 and the coordinates of the overworld portal were 269, 68, -309.
2. Create nether portal and enter it.
3. Cause a game crash (or close the game?) during the generation of the Nether.
4. There should be no Nether Portal in the Nether for you to return to the overworld with.