gl_rasterizer: Fix buffers without size

On NVN buffers can be enabled but have no size. According to deko3d and
the behavior we see in Animal Crossing: New Horizons these buffers get
the special address of 0x1000 and limit themselves to 0xfff.

Implement buffers without a size by binding a null buffer to OpenGL
without a side.

https://github.com/devkitPro/deko3d/blob/1d1930beea093b5a663419e93b0649719a3ca5da/source/maxwell/gpu_3d_vbo.cpp#L62-L63