Code review comment for lp://qastaging/~afrantzis/mir/texture-bindable

Looks sensible.

Non-blocking: It might be nice to provide TextureBindable* as_texture_bindable(mg::Buffer*) as a helper method; the logic seems duplicated enough to warrant it.

It would also make it easier to play with different ways of extracting the TextureBinadble (dynamic_cast, our own hand-rolled RTTI, whatever). Should we find that we want to do so.