VertexBuffer::render will fail if setProgram or setAutoProgram is not called

Basically, PrivateVertexBuffer::render requires either a program to be set or AutoProgram to return something, otherwise it just prints "no program defined!" to the tty on every frame. That's not really such a great outcome. It probably makes sense to have a generic pass-through program by default and then warn about unfound uniform and attribute bindings.