[Win32] Avoid unnecessary handle creation for image of ImageGcDrawer

With an Image based on an ImageGcDrawer, a call to #getImageData() will
always create a handle for the requested zoom. For all other kinds of
images, this will at most create a temporary handle and only cache the
image data to avoid unnecessary handles for zooms you may never need.

This change adapts the ImageGcDrawerWrapper implementation to not create
a handle when requesting image data for a zoom for which no handle
exists yet.

Author: HeikoKlare

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/graphics/Image.java

@@ -2789,11 +2789,10 @@ ImageData newImageData(int zoom) {
 
 	@Override
 	protected ElementAtZoom<ImageData> loadImageData(int zoom) {
-		return new ElementAtZoom<>(getImageMetadata(new ZoomContext(zoom)).getImageData(), zoom);
+		return new ElementAtZoom<>(loadImageData(new ZoomContext(zoom)), zoom);
 	}
 
-	@Override
-	protected DestroyableImageHandle newImageHandle(ZoomContext zoomContext) {
+	private ImageData loadImageData(ZoomContext zoomContext) {
 		currentZoom = zoomContext;
 		int targetZoom = zoomContext.targetZoom();
 		int gcStyle = drawer.getGcStyle();
@@ -2813,14 +2812,18 @@ protected DestroyableImageHandle newImageHandle(ZoomContext zoomContext) {
 			drawer.drawOn(gc, width, height);
 			ImageData imageData = image.getImageData(targetZoom);
 			drawer.postProcess(imageData);
-			ImageData newData = adaptImageDataIfDisabledOrGray(imageData);
-			return init(newData, targetZoom);
+			return adaptImageDataIfDisabledOrGray(imageData);
 		} finally {
 			gc.dispose();
 			image.dispose();
 		}
 	}
 
+	@Override
+	protected DestroyableImageHandle newImageHandle(ZoomContext zoomContext) {
+		return init(loadImageData(zoomContext), zoomContext.targetZoom);
+	}
+
 	@Override
 	Object getProvider() {
 		return drawer;