[slidingpopups] Only remove WindowClosedGrabRole if the effect owns the grab

Summary:
The effect unset the WindowClosedGrabRole unconditionally if it does not
manage the window. This results in any grab set by other effects to break.

BUG: 376609
FIXED-IN: 5.9.5

Reviewers: #kwin, #plasma

Subscribers: plasma-devel, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D5225

effects/slidingpopups/slidingpopups.cpp

@@ -360,7 +360,9 @@ void SlidingPopupsEffect::slotPropertyNotify(EffectWindow* w, long a)
 
     if (data.length() < 1) {
         // Property was removed, thus also remove the effect for window
+        if (w->data(WindowClosedGrabRole).value<void *>() == this) {
             w->setData(WindowClosedGrabRole, QVariant());
+        }
         delete mAppearingWindows.take(w);
         delete mDisappearingWindows.take(w);
         mWindowsData.remove(w);