wIconChangeImageFile set the file image

The function wIconChangeImageFile set the file_image variable directly,
now the code is faster and the assigned image is used.

Before this patch, the assigned file couldn't be used, because wIconUpdate
serached the icon using different methods.

src/icon.c

@@ -398,9 +398,8 @@ Bool wIconChangeImageFile(WIcon *icon, char *file)
 		unset_icon_image(icon);
 
 		/* Set the new image */
-		icon->file_image = image;
 		icon->file = wstrdup(path);
-		wIconUpdate(icon, NULL);
+		wIconUpdate(icon, image);
 	} else {
 		error = 1;
 	}