UsbPlayerTest.unmuteTest third Case correction of the Production Code

src/main/java/device/usbPlayer/UsbPlayer.java

@@ -193,6 +193,7 @@ public class UsbPlayer implements Device {
     public String unmute() {
 
         setLautstaerke(soundWas);
+        this.soundWas = 0;
         return "unmuted";
     }