Initialize XImage struct fully

I was getting sporadic failures from XInitImage (causing the raster
backend to not draw anything).

BUG=skia:

Change-Id: Ied79f2b5354d89c146aca64d70fde8cf9f3ab62e
Reviewed-on: https://skia-review.googlesource.com/9102
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed