glamor woes with nouveau

[Olivier Fourdan]

Hey!

So I was wrong (again), this is not glamor_composite_choose_shader()
failed which is the problem, the rendering issue comes from
glamor_poly_fill_rect_gl() (the plain ackground is garbled, not the
actual content, if that makes any sense).

If I force glamor_poly_fill_rect_bail() from glamor_poly_fill_rect()
rendering is fine.

It is also worth noting that the glsl version on this particular
hardware is 120, so we are using glamor_facet_polyfillrect_120...

I also noticed that not showing the GtkEntry box avoids the issue, but
I can't make sense of that.

Still digging, meanwhile if someone else has an idea :)

Cheers,
Olivier