os: Ignore dying client in ResetCurrentRequest

You might as well, it's harmless. Better, some cleanup code (like DRI2
swap wait) needs to run both normally and at client exit, so it
simplifies the callers to not need to check first. See 4308f5d3 for a
similar example.

Props: @ajax (Adam Jackson)

Fixes: xorg/xserver#211

Signed-off-by: Daniel Llewellyn <diddledan@ubuntu.com>
3 jobs for allow-empty-client-for-iglx in 7 minutes (queued for 3 seconds)
Status Job ID Name Coverage
  Docker Image
passed #1501544
debian-testing

00:00:20

 
  Build And Test
passed #1501545
autotools-build-and-test

00:06:40

passed #1501546
meson-build-and-test

00:02:30