gl_rasterizer: Fixup for #1723.

On invalidating the streaming buffer, we need to reupload all vertex buffers.
But we don't need to reconfigure the vertex format.
This was a (silly) misstake in #1723.

Thanks at Rodrigo for discovering the issue.

Fun fact, as configuring the vertex format also invalidate the vertex buffer,
this misstake had no affect on the behavior.