remove deleted windows from motionmanagers

Eg. if a window is closed while "timeline.currentValue() == 0",
slotWindowClosed() will shortcut exit and not be removed from the
managers, thus dangle around forever.

Maybe there're other ways for a window to be deleted w/o
the closed slot being entered.

CCBUG: 339970
REVIEW: 126034

effects/desktopgrid/desktopgrid.cpp

@@ -422,6 +422,12 @@ void DesktopGridEffect::slotWindowDeleted(EffectWindow* w)
             break;
         }
     }
+    if (isUsingPresentWindows()) {
+        for (QList<WindowMotionManager>::iterator it = m_managers.begin(),
+                                                 end = m_managers.end(); it != end; ++it) {
+            it->unmanage(w);
+        }
+    }
 }
 
 void DesktopGridEffect::slotWindowGeometryShapeChanged(EffectWindow* w, const QRect& old)