Typing seed 0 no longer generates a random seed

The bug

If you put 0 in the seed box where you type the seed, the seed will always be 48 instead of a random seed. It looks like this issue has been introduced with the fix for MC-183786.

How to reproduce

1. Create a new world
2. Go to the "More World Options" screen
3. Type "0" in the seed field
4. Create the world
5. Run /seed
   → Notice how the seed is 48 and not a random value

Notes

The 0 turning into 48 in codes of customized worlds is MC-184634.