Issue #301 - [win32]: device dependent bitmaps (DDBs) are always opaque

DDBs can have a 32 bit depth but the returned alpha channel data is always 0 which means fully
transparent. Since we want to avoid a costly blit operation from 32 to 24 bits, stripping the alpha
channel data, we set the alpha channel data to 255 for better compatibility. Note that alpha channel
data in ImageData.data should always be ignored anyway and be read from ImageData.alphaData instead.

Author: jonathan-meier

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

@@ -1616,10 +1616,10 @@ public ImageData getImageDataAtCurrentZoom() {
 			/* Construct and return the ImageData */
 			ImageData imageData = new ImageData(width, height, depth, palette, 4, data);
 			imageData.transparentPixel = this.transparentPixel;
-			if (isDib && depth == 32) {
+			if (depth == 32) {
 				byte straightData[] = new byte[imageSize];
 				byte alphaData[] = new byte[width * height];
-				boolean validAlpha = true;
+				boolean validAlpha = isDib;
 				for (int ap = 0, dp = 0; validAlpha && ap < alphaData.length; ap++, dp += 4) {
 					int b = data[dp    ] & 0xFF;
 					int g = data[dp + 1] & 0xFF;