EffectComposer: Fix effect preview zoom

Zoom must scale the component showing the preview, not the source
image. This way the effect stays consistent regardless of the zoom
level.

Fixes: QDS-11899
Change-Id: I550eb9ff693c24a853f5c25d9d79fa146448663f
Reviewed-by: Mahmoud Badri <mahmoud.badri@qt.io>

src/plugins/effectcomposer/effectcomposermodel.h

@@ -178,7 +178,7 @@ private:
     QList<CompositionNode *> m_nodes;
 
     int m_selectedIndex = -1;
-    bool m_isEmpty = true;
+    bool m_isEmpty = false;  // Init to false to force initial bake after setup
     bool m_hasUnsavedChanges = false;
     // True when shaders haven't changed since last baking
     bool m_shadersUpToDate = true;