[MC-277713] If a font file points to a nonexistent texture, all resource packs get unloaded

If a font file points to a texture file which does not exist, all resource packs will get unloaded.

This behaviour first occurs in 23w17a - it was not present from 1.13-pre7 to 23w16a.

Behaviour in 23w16a:

Behaviour from 23w17a to present:

A resource pack that demonstrates this attached to this ticket.

Applying this resource pack would not unload all loaded resource packs, but just throw an error in the log like in previous versions.

Everything gets unloaded.