In geometry shaders, calling EmitVertex() makes the contents of all
output variables undefined. We need to rewrite our layer ID and view
index outputs before each EmitVertex() call; assuming they'll preserve
their values is undefined behavior.
Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28067>