Ignore undefined all-zero alpha data for 32-bit icons without mask

On Windows, GetDIBits() may return undefined alpha bytes for 32-bit
BI_RGB bitmaps, commonly resulting in all-zero alpha even for fully
opaque images.

When icon mask data is missing, this caused opaque icons to be
incorrectly treated as fully transparent.

Reject all-zero alpha data and only replace empty mask data when the
alpha channel contains meaningful (non-opaque, non-zero) values.

Author: ShahzaibIbrahim

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

@@ -3142,12 +3142,14 @@ public ImageData getImageData() {
 					if (!hasMaskData && depth == 32) {
 						alphaData = new byte[width * height];
 						boolean hasAlphaData = false;
+						boolean isAllZeroAlpha = true;
 						for (int pixelIndex = 0; pixelIndex < alphaData.length; pixelIndex++) {
 							alphaData[pixelIndex] = data[pixelIndex * 4 + 3];
 							hasAlphaData |= alphaData[pixelIndex] != -1;
+							isAllZeroAlpha &= alphaData[pixelIndex] == 0;
 						}
 						// In case there is alpha data, replace the empty mask data with proper alpha data
-						if (hasAlphaData) {
+						if (hasAlphaData && !isAllZeroAlpha) {
 							maskData = null;
 						} else {
 							alphaData = null;