audio: Bug fix: alGenBuffer accepts only positive number

exp/audio/audio_openal.go

@@ -132,13 +132,15 @@ func (p *player) play() error {
 	// TODO: What if play is already called?
 	emptyBytes := make([]byte, bufferSize)
 	m.Lock()
-	queued := p.alSource.BuffersQueued()
-	bufs := al.GenBuffers(8 - int(queued))
+	n := 8 - int(p.alSource.BuffersQueued())
+	if 0 < n {
+		bufs := al.GenBuffers(n)
 		for _, buf := range bufs {
 			// Note that the third argument of only the first buffer is used.
 			buf.BufferData(al.FormatStereo16, emptyBytes, int32(p.sampleRate))
 			p.alSource.QueueBuffers(buf)
 		}
+	}
 	al.PlaySources(p.alSource)
 	m.Unlock()
 	go func() {