Minecraft does not create world icon if it is missing

Minecraft does not create a world icon if it is missing but also disables the "Reset Icon" button.

There are two cases in which a world can have no icon:

1. The world was generated in a previous version
2. You close the a newly generated world before entering:
   1. Create a new world
   2. Minimize Minecraft
   3. Open Minecraft after it finished generating the world and exit back to the main menu