Broken transparency handling for shell icons

[HeikoKlare]

Mirror ticket for:

• Application icon doesn't render after upgrading eclipse-platform/eclipse.platform.swt#2638

Reproducer:

import org.eclipse.swt.graphics.*;
import org.eclipse.swt.widgets.*;

public class ImageWithNoTransparencyMaskOnShell {
    public static void main(String[] args) {
    	System.setProperty("swt.autoScale.updateOnRuntime", "true");
    	System.setProperty("swt.autoScale", "quarter");
        Display display = new Display();
        Shell shell = new Shell(display);
        shell.setText("Image With No Transparency Mask on Shell");
        shell.setSize(600, 600);
		Image image = new Image(display, ButtonWithGifImage.class.getResourceAsStream("png-image.png"));
		shell.setImage(image);

        shell.open();
        while (!shell.isDisposed()) {
            if (!display.readAndDispatch())
                display.sleep();
        }

        image.dispose();
        display.dispose();
    }
}