Early Loading system does not fall back to default `earlyWindowProvider` when the one set in the config does not exist

[Keksuccino]

Minecraft Version: 1.21.1
NeoForge Version: 21.1.218

Description of issue:

When you set a custom earlyWindowProvider in /config/fml.toml, NeoForge will not correctly fall back to fmlearlywindow when the one set in the config is not available/valid anymore.

Expected behavior:

When it fails to load/init the custom provider, it should fall back to the default provider.

Related issues:

• When the mod Drippy-Early-Loading-Screen is removed, the NeoForge early loading screen disappears. Keksuccino/Drippy-Loading-Screen#105
• default neoforge early loading screen becomes unavailable once the Early LS module is removed Keksuccino/Drippy-Loading-Screen#107