Don't reset viewport if binding framebuffer for reading only.
Don't reset viewport if binding framebuffer for reading only.

Caused assertion. Anyway, I need to clean up that mess with framebuffer
binding. Nobody needs to bind it for reading.

ashimidashajia/magnum,DerThorsten/magnum,MiUishadow/magnum,MiUishadow/magnum,ashimidashajia/magnum,DerThorsten/magnum,MiUishadow/magnum,ashimidashajia/magnum,DerThorsten/magnum,MiUishadow/magnum,ashimidashajia/magnum,MiUishadow/magnum,DerThorsten/magnum,DerThorsten/magnum,ashimidashajia/magnum,MiUishadow/magnum