FIX: image's alpha channel not right

Author: bitbegin

runtime/image-utils.reds

@@ -219,7 +219,7 @@ image-utils: context [
 		src.h: as float! sh
 		size: rect.w * rect.h * 4
 		rgba: as int-ptr! allocate size
-		set-memory as byte-ptr! rgba #"^(FF)" size
+		set-memory as byte-ptr! rgba #"^(00)" size
 		i: 0 j: 0
 		loop rect.h [
 			i: 0

runtime/platform/image-gdk.reds

@@ -296,9 +296,7 @@ OS-image: context [
 			b: p/1
 			p/1: p/3
 			p/3: b
-			either alpha? [
-				p/4: #"^(FF)" - p/4
-			][
+			unless alpha? [
 				p/4: #"^(FF)"
 			]
 			dst/offset: old