Always assign a new buffer when requested to
Always assign a new buffer when requested to

Rather than trying to second-guess the server by both only occasionally
creating buffers, and mashing devPrivate.ptr directly rather than using
ModifyPixmapHeader.

Signed-off-by: Daniel Stone <3d0f3b9ddcacec30c4008c5e030e6c13a478cb4f@fooishbar.org>

gcampax/xf86-video-wlshm,gcampax/xf86-video-wlshm