This causes glDrawArrays to fail in core profile, and thus on OS X, see:
http://renderingpipeline.com/2012/03/attribute-less-rendering/
There must be something bound, even though it is not used.
Fixes#7599. I'm not sure this is actually the best way to fix it,
since AFAICT it makes a nonobvious assumption that *something* will be
bound before the first attributeless rendering in
TextureConverter::DecodeToTexture, but it's what degasus suggested and
seems to work.
comex
b48e059173