broadway: Correct handling of opaque colors

If alpha is 255, we use rgb() instead of rgba(), not if alpha is 0.
This makes the title bar gradient go from fully transparent to blue
rather than black to blue..

gdk/broadway/broadway.js

@@ -396,7 +396,7 @@ TransformNodes.prototype.decode_color = function() {
     var g = (rgba >> 8) & 0xff;
     var b = (rgba >> 0) & 0xff;
     var c;
-    if (a == 0)
+    if (a == 255)
         c = "rgb(" + r + "," + g + "," + b + ")";
     else
         c = "rgba(" + r + "," + g + "," + b + "," + (a / 255.0) + ")";