Halloween Mash-up pack world template is always created in Survival mode

Steps to reproduce:

1. Ensure you own the Halloween Mash-up pack
2. Create a new world with the Halloween Mash-up world template in a game mode other than Survival

Observed result:
You spawn in Survival mode.

Expected result:
You spawn in the selected game mode.

Notes:
This may apply to other mash-up pack world templates as well.