Don't abort if /etc/pulse/client.conf is inaccessible

On systems without PulseAudio, rr currently aborts. Change
create_pulseaudio_config() so it indicates to its caller that no
replacement configuration settings should be used instead, and
continue executing.

Signed-off-by: Stephen Kitt <steve@sk2.org>
Merge pull request #1037 from skitt/master

Don't abort if /etc/pulse/client.conf is inaccessible