shiny/driver/x11driver: don't unswizzle buffers that aren't re-used.

It's just needless work.

Change-Id: I60821b51391bf9392ef1b015cd4524d8ad1bf93c
Reviewed-on: https://go-review.googlesource.com/14841
Reviewed-by: David Crawshaw <crawshaw@golang.org>
2 files changed