The bug

If a resource pack contains an invalid image file as the grass or foliage colormap file, applying this resource pack will cause an error and force all other resource packs to unload.

This is an extreme response to an image being invalid - all other cases of this simply cause that texture file to become the "missing texture" in-game.

How to reproduce

A resource pack that replaces grass.png with an invalid image file is attached to this ticket.

Expected results

Applying this resource pack would not unload all other resource packs.

Actual results

It does.

Further notes

I've also attached a resource pack that replaces the colormap with the missing texture to show the expected results for applying the main resource pack.