always defer delete of Deleted to next event cycle

BUG: 317765
FIXED-IN: 4.11
REVIEW: 110756

deleted.cpp

@@ -107,16 +107,15 @@ void Deleted::copyToDeleted(Toplevel* c)
     }
 }
 
-void Deleted::unrefWindow(bool delay)
+void Deleted::unrefWindow()
 {
     if (--delete_refcount > 0)
         return;
-    // needs to be delayed when calling from effects, otherwise it'd be rather
-    // complicated to handle the case of the window going away during a painting pass
-    if (delay)
-        deleteLater();
-    else
-        delete this;
+    // needs to be delayed
+    // a) when calling from effects, otherwise it'd be rather complicated to handle the case of the
+    // window going away during a painting pass
+    // b) to prevent dangeling pointers in the stacking order, see bug #317765
+    deleteLater();
 }
 
 int Deleted::desktop() const

deleted.h

@@ -37,7 +37,7 @@ public:
     static Deleted* create(Toplevel* c);
     // used by effects to keep the window around for e.g. fadeout effects when it's destroyed
     void refWindow();
-    void unrefWindow(bool delay = false);
+    void unrefWindow();
     void discard();
     virtual int desktop() const;
     virtual QStringList activities() const;

effects.cpp

@@ -1662,7 +1662,7 @@ void EffectWindowImpl::refWindow()
 void EffectWindowImpl::unrefWindow()
 {
     if (Deleted* d = dynamic_cast< Deleted* >(toplevel))
-        return d->unrefWindow(true);   // delayed
+        return d->unrefWindow();   // delays deletion in case
     abort(); // TODO
 }