output: delay reopen after device failure

When one of several output devices failed, MPD tried to reopen it
quite often, wasting a lot of resources.  This patch adds a delay:
wait 10 seconds before retrying.  This might be changed to exponential
delays later, but for now, it makes the problem go away.

src/audio.c

@@ -342,6 +342,7 @@ int enableAudioDevice(unsigned int device)
 	if (device >= audioOutputArraySize)
 		return -1;
 
+	audioOutputArray[device].reopen_after = 0;
 	audioOutputArray[device].enabled = true;
 	idle_add(IDLE_OUTPUT);