Font atlas memory leak

[andreymal]

loop {
    load_ttf_font("./font.ttf").await?;
}

Both system RAM and GPU memory are leaking.

I tried to implement Drop for Atlas like in 65451f5:

impl Drop for Atlas {
    fn drop(&mut self) {
        get_context().quad_context.delete_texture(self.texture);
    }
}

and this fixed the leak (but I'm not sure if this solution is complete and/or correct)