add a missing exit()

tools/fimg2png.c

@@ -92,6 +92,7 @@ if (2 != argc-optind) {
 foo = convertir_fimg_en_PNG(argv[optind], argv[optind+1], to_gray);
 if (foo) {
 	fprintf(stderr, "%s : got a %d from convertor\n", argv[0], foo);
+	exit(1);
 	}
 
 return 0;