[PATCH xserver] exa: Use PictureMatchFormat for source-only picture format description

[Adam Jackson]

On Fri, 2018-06-01 at 11:58 +0200, Michel Dänzer wrote:
> From: Michel Dänzer <michel.daenzer at amd.com>
> 
> Their pFormat member is NULL, which resulted in a crash in
> miRenderColorToPixel.
> 
> Fixes: 8171d4c2d67b "render: Store and use all 16bpc of precision for
>                      solid pixels (v2.1)"
> Signed-off-by: Michel Dänzer <michel.daenzer at amd.com>

I'm not entirely sure why a source-only picture would have ->format but
not ->pFormat? Still, if that's the case, this would definitely be a
correct fix, so.

Reviewed-by: Adam Jackson <ajax at redhat.com>

- ajax