Inconsistency: You cannot use a biome by double-clicking in the single biome customization screen

When you double-click a biome in the single biome customization screen, you only choose the biome, not use it. This is inconsistent with other selection screens (world, server, language etc).

Steps to Reproduce:

1. Go to the 'Create New World' screen
2. Go to the 'World' tab
3. Change world type to 'Single Biome'
4. Click 'Customize'
5. Double click on any of the biome entries.

Expected & Observed:

The player cannot double click to select one of the biomes. Instead, they simply highlight it and stay on the biome select screen.