Fix: Headphones do not mute speakers in XFCE Linux desktop

Some time ago, I switched from Fluxbox to XFCE in my primary operating system, Arch Linux. I noticed a weird behavior related to the sound system. I have no pulseaudio, only ALSA. When I plugged in headphones, the speakers were not muted. Before installing XFCE, this worked like a charm. Here is a simple solution for this issue.