fast-fail in as_bind_group

[robtfm]

Objective

prevent gpu buffer allocations when running as_bind_group for assets with texture dependencies that are not yet available.

Solution

reorder the binding creation so that fallible items are created first.

[robtfm]

this is an improvement but i should note: we still potentially create some textures before discarding them, if earlier images in the binding_impls order are available and later ones are not.

it would be a little more involved to gather all the required handles before creating any gpu resources but probably worthwhile.