[effects/magiclamp] Eliminate unnecessary reallocations

Summary:
The maximum size of `newQuads` is known in advance, so we can avoid
unnecessary reallocations when adding transformed window quads to
`newQuads`.

Test Plan: Minimized/unminimized System Settings.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: davidedmundson, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D14117

effects/magiclamp/magiclamp.cpp

@@ -198,6 +198,7 @@ void MagicLampEffect::paintWindow(EffectWindow* w, int mask, QRegion region, Win
                                                                             quad[3]._SET_B_(quad[3]._B_() + offset[_O3_])
 
         WindowQuadList newQuads;
+        newQuads.reserve(data.quads.count());
         float quadFactor;   // defines how fast a quad is vertically moved: y coordinates near to window top are slowed down
                             // it is used as quadFactor^3/windowHeight^3
                             // quadFactor is the y position of the quad but is changed towards becomming the window height