xgb-image: seek 32-bit visuals along with 30-bit

We only tried to upgrade to 32-bit depth when we weren't looking
for 30-bit visuals.  Probably of no practical consequence.

prototypes/xgb-image.go

@@ -117,14 +117,15 @@ func main() {
 	// the backpixel value. (And we reject it in 30-bit depth anyway.)
 	for _, i := range screen.AllowedDepths {
 		for _, v := range i.Visuals {
-			// TODO: Could/should check other parameters.
+			// TODO: Could/should check other parameters, e.g., the RGB masks.
 			if v.Class != xproto.VisualClassTrueColor {
 				continue
 			}
-			if prefer30 && i.Depth == 30 ||
-				!prefer30 && i.Depth == 32 {
+			if i.Depth == 32 || i.Depth == 30 && prefer30 {
 				visual, depth = v.VisualId, i.Depth
-				break
+				if !prefer30 || i.Depth == 30 {
+					break
+				}
 			}
 		}
 	}