return an error code when needed

tools/fimg2text.c

@@ -169,6 +169,7 @@ if (1 != argc-optind) {
 foo = convertir_fimg_en_machinable(argv[optind], "-", steps, norm_val);
 if (foo) {
 	fprintf(stderr, "%s : got a %d from convertor\n", argv[0], foo);
+	return 1;
 	}
 
 return 0;