Fix resource leaks and minor issues

- Close pipe fds on fork failure in ExecFile::execute
- Add exception-safe fclose in cmd_file_append via try/catch
- Add overflow guards before K/M/G bit shifts in parse_whole_value
- Fix %u format for int* in sscanf (change to %d)
- Fix typo "atter"→"after" in error message

src/option_parser.cc

@@ -137,7 +137,7 @@ void
 OptionParser::call_int_pair(slot_int_pair slot, const std::string& arg) {
   int a, b;
 
-  if (std::sscanf(arg.c_str(), "%u-%u", &a, &b) != 2)
+  if (std::sscanf(arg.c_str(), "%d-%d", &a, &b) != 2)
     throw std::runtime_error("Invalid argument, \"" + arg + "\" should be \"a-b\"");
 
   slot(a, b);