Do full repaints on window damage in boxswitch with GLES

Due to changes in the blur effect, the EffectFrame was flickering
with GLES. This can be worked around by doing full repaints whenever
a window is damagded while boxswitch is active with GLES. The problem
only occurs with the GLES backend due to the way how the buffers are
swapped.
BUG: 272688

effects/boxswitch/boxswitch.cpp

@@ -272,6 +272,10 @@ void BoxSwitchEffect::slotWindowDamaged(EffectWindow* w, const QRect& damage)
                 effects->addRepaint(desktops[ w->desktop()]->area);
             }
         }
+#ifdef KWIN_HAVE_OPENGLES
+        // without full repaints, blur effect flickers on GLES, see BUG 272688
+        effects->addRepaintFull();
+#endif
     }
 }