rots-util: return -1 for unknown options

source/sign.c

@@ -48,7 +48,7 @@ static int parse_args(struct args *args, int argc, char *argv[])
 		case OPTION_DIGEST: args->digest = optarg; break;
 		case OPTION_KEY: args->key = optarg; break;
 		case OPTION_CERT: args->cert = optarg; break;
-		default: break;
+		default: return -1;
 		}
 	}
 

source/verify.c

@@ -44,7 +44,7 @@ static int parse_args(struct args *args, int argc, char *argv[])
 		case OPTION_HELP: return -1;
 		case OPTION_IMAGE: args->image = optarg; break;
 		case OPTION_CERTS: args->certs = optarg; break;
-		default: break;
+		default: return -1;
 		}
 	}