abrasive/shairport — pull request #224 by plietar (2013-06-09 18:38:27+00:00)
Title: Fix libao output driver.

The driver id returned by libao wasn't checked correctly.
When the driver did not exist, libao returns a negative number. The
libao output driver checked for a non zero id.
This caused shairport to refuse to use the first driver, and not fail
when using a non-existant driver.