Don't repaint the Canvas if it's just changing position.

Task-number: QTBUG-33005

Change-Id: I94613c0a0e066798800e068aee7c6288fce54dbd
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>

src/quick/items/context2d/qquickcanvasitem.cpp

@@ -597,7 +597,7 @@ void QQuickCanvasItem::geometryChanged(const QRectF &newGeometry, const QRectF &
         emit canvasWindowChanged();
     }
 
-    if (d->available)
+    if (d->available && newSize != oldGeometry.size())
         requestPaint();
 }