Moved `gl::BindBuffer` outside unsafe block
Moved `gl::BindBuffer` outside unsafe block

Closes https://github.com/PistonDevelopers/rust-graphics/issues/526

PistonDevelopers/graphics,andrewcsmith/graphics,echochamber/graphics,Vinatorul/graphics,stjahns/graphics,bvssvni/graphics,mitchmindtree/graphics,aepsil0n/graphics