fix bug in BitmapEx::operator==

Just because this image is transparent, does not mean it is equal to the
other image.

Similarly, just because this image has transparency color, does not mean
the other image has valid transparency color.

Also move the cheaper mbAlpha check before the more expensive
ShallowEquals check.

there since
    commit 8ab086b6
    Date:   Mon Sep 18 16:07:07 2000 +0000
    initial import

Change-Id: I63033bc8e7fed991513a171e637768e826eafad9
Reviewed-on: https://gerrit.libreoffice.org/71572
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

vcl/source/gdi/bitmapex.cxx

@@ -187,13 +187,17 @@ bool BitmapEx::operator==( const BitmapEx& rBitmapEx ) const
     if (GetSizePixel() != rBitmapEx.GetSizePixel())
         return false;
 
-    if (meTransparent == TransparentType::NONE)
-        return true;
+    if (meTransparent != rBitmapEx.meTransparent)
+        return false;
 
-    if (meTransparent == TransparentType::Color)
-        return maTransparentColor == rBitmapEx.maTransparentColor;
+    if (meTransparent == TransparentType::Color
+        && maTransparentColor != rBitmapEx.maTransparentColor)
+        return false;
+
+    if (mbAlpha != rBitmapEx.mbAlpha)
+        return false;
 
-    return maMask.ShallowEquals(rBitmapEx.maMask) && mbAlpha == rBitmapEx.mbAlpha;
+    return maMask.ShallowEquals(rBitmapEx.maMask);
 }
 
 bool BitmapEx::IsEmpty() const