Verify load-placeholder Images in Import

[Aadjou]

There were some lightmap bake tasks that had pink color bleeding from (possibly) missing textures.

Verify that loading placeholder images work as intended.

References commit 4156d11

[ghost]

i think if we fix https://github.com/archilogic-com/services/issues/35 it will fix this

[Aadjou]

loading placeholder images is a feature of this addon, so we should make sure that it actually works generally and add a catch to load a placeholder if the input image is 0kb