Textures are silently not saved if pillow is not installed

[Altren]

Followng code works without any warnings or suggestions that something is wrong:

mesh = trimesh.load("mesh.obj"). # load obj with textures
_ = m.export("mesh.glb")

But it does not save any textures. It took me a while to figure out that pillow dependency is silently missing

[mikedh]

Hey, it's actually printing a log.debug message which is a little buried admittedly, if we changed it to a log.warning it would be a lot more obvious but spam users pretty hard. I usually run with trimesh.util.attach_to_log() while debugging, I should check to make sure that's in the developers guide somewhere obvious.