Use FAIL as the default dest if unable to parse

src/main.zig

@@ -86,7 +86,7 @@ fn parseDest(in: ?[]const u8) ![4]u8 {
         const addr = try std.net.Ip4Address.parse(dest, 0);
         return @bitCast(addr.sa.addr);
     }
-    return .{ 70, 70, 70, 70 };
+    return "FAIL".*;
 }
 
 const builtin = @import("builtin");