Regression: power-manager wakes up locked display on message notification

Hello,

recent versions of xfce4-power-manager wake up my locked display when I receive a message on Discord. It appears to be caused by !22 (merged). When that commit is reverted on 4.18.0, the behavior stops. Unfortunately this was obscure enough that I wasn't able to track down the cause before 4.18 was released :(

This is likely the combination of multiple issues:

• My screensaver/locker is xsecurelock. It will put displays to sleep when initially locking, but not when they were woken by other applications (which is likely hard/impossible to detect). As a result they stay active indefinitely afterwards. I have also created this issue.
• Discord (Linux version) is using Electron, i.e. it's a website + Chrome browser disguised as an "application". Naturally this results in all kinds of hijinks. Likely the brief notification sound is enough to trigger Chrome's "media playback -> inhibit screensaver" logic. Discord is about 0.0000% likely to fix this.

It would be great if xfce4-power-manager could re-evaluate this commit. It seems to cause side-effects. Maybe only react to inhibit events that last longer than a few seconds?

Thanks!