Use correct flag when checking whether a scene window is opaque

Summary:
Given that allclips contains opaque regions of higher windows, we should
check PAINT_WINDOW_TRANSLUCENT flag instead of PAINT_WINDOW_TRANSFORMED.

ba39d1f917 introduced that check. Neither
the commit message nor the associated review have any comments regarding
checking PAINT_WINDOW_TRANSFORMED, so given the following comment

    // Here we rely on WindowPrePaintData::setTranslucent() to remove
    // the clip if needed.

PAINT_WINDOW_TRANSFORMED is most likely a typo.

Reviewers: #kwin, graesslin

Reviewed By: #kwin, graesslin

Subscribers: graesslin, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D18236

scene.cpp

@@ -345,7 +345,7 @@ void Scene::paintSimpleScreen(int orig_mask, QRegion region)
 
         // Here we rely on WindowPrePaintData::setTranslucent() to remove
         // the clip if needed.
-        if (!data->clip.isEmpty() && !(data->mask & PAINT_WINDOW_TRANSFORMED)) {
+        if (!data->clip.isEmpty() && !(data->mask & PAINT_WINDOW_TRANSLUCENT)) {
             // clip away the opaque regions for all windows below this one
             allclips |= data->clip;
             // extend the translucent damage for windows below this by remaining (translucent) regions