aplay: change if statement to else if in xrun function

alsa-project/alsa-utils pull request #50 was opened from JSFamily:

Request URL : https://github.com/alsa-project/alsa-utils/pull/50 Patch URL : https://github.com/alsa-project/alsa-utils/pull/50.patch Repository URL: https://github.com/alsa-project/alsa-utils