eolian: help and version shall not cause an error exit status

eolian_gen called with --help or --version is a valid action. It shall
terminates with the 0 exit status.

src/bin/eolian/main.c

@@ -460,9 +460,11 @@ main(int argc, char **argv)
           break;
         case 'h':
           _print_usage(argv[0], stdout);
+          pret = 0;
           goto end;
         case 'v':
           _print_version(stdout);
+          pret = 0;
           goto end;
         default:
           _print_usage(argv[0], stderr);