Use-after-free crash if shader is dropped while program is in use

[Bash-09]

The current triangle example code uses this to construct the shader program:

    let shader = shader::Library::from_bytes(SHADER_BYTES).unwrap();
    let vertex_shader = shader.get(0).unwrap();
    let program = shader::Program::new(vertex_shader).unwrap();

When changed to this:

    let program = {
        let shader = shader::Library::from_bytes(SHADER_BYTES).unwrap();
        let vertex_shader = shader.get(0).unwrap();
        shader::Program::new(vertex_shader).unwrap()
    };

shader is dropped which causes the internal *mut ctru_sys::DVLB_s to be freed. I believe this is required to stay alive while the Program is in use, I think its Entrypoint is used to bind uniforms and run the shader etc.

With the second version of the above code I was getting a crash due to a memory read error in libctru::DVLE_GetUniformRegister which had been called by citro3d::Shader::get_uniform.