audio: Add test for negative position

audio/loop.go

@@ -60,6 +60,9 @@ func (i *InfiniteLoop) Seek(offset int64, whence int) (int64, error) {
 	case io.SeekEnd:
 		return 0, fmt.Errorf("audio: whence must be io.SeekStart or io.SeekCurrent for InfiniteLoop")
 	}
+	if next < 0 {
+		return 0, fmt.Errorf("audio: position must >= 0")
+	}
 	next %= i.size
 	pos, err := i.stream.Seek(next, io.SeekStart)
 	if err != nil {

audio/loop_test.go

@@ -72,4 +72,9 @@ func TestInfiniteLoop(t *testing.T) {
 			t.Errorf("index: %d, got: %v, want: %v", i, got, want)
 		}
 	}
+
+	// Seek to negative position is an error.
+	if _, err := l.Seek(-1, io.SeekStart); err == nil {
+		t.Errorf("got: %v, want: %v", err, nil)
+	}
 }