Issue #301 - [win32]: only allow alpha data in ImageData.data for icons

Fixes the regression introduced in PR #224 (commit 8def011) which
also allowed alpha data in ImageData.data for bitmaps. Alpha data for bitmaps must be provided in
ImageData.alphaData. This ensures proper conversion of the image data to pre-multiplied alpha format
and aligns the behavior of Image initialization with the implementation for Linux.

Author: Eclipse Releng Bot

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

@@ -1862,7 +1862,11 @@ static ImageData directToDirect(ImageData src, int newDepth, PaletteData newPale
 					}
 					break;
 				case 32:
-					if (!(redMask == 0xFF00 && greenMask == 0xFF0000 && blueMask == 0xFF000000)) {
+					if (i.getTransparencyType() != SWT.TRANSPARENCY_MASK) {
+						newDepth = 24;
+						newPalette = new PaletteData(0xFF, 0xFF00, 0xFF0000);
+					}
+					else if (!(redMask == 0xFF00 && greenMask == 0xFF0000 && blueMask == 0xFF000000)) {
 						newPalette = new PaletteData(0xFF00, 0xFF0000, 0xFF000000);
 					}
 					break;