FileManager: Improve error handling when posix_spawn() fails

Previously we'd try to disown() the newly created process even if
posix_spawn() had failed.

Userland/Applications/FileManager/DirectoryView.cpp

@@ -507,15 +507,18 @@ void DirectoryView::launch(URL const&, LauncherHandler const& launcher_handler)
  posix_spawn_file_actions_addchdir(&spawn_actions, path().characters());
 
  char const* argv[] = { launcher_handler.details().name.characters(), nullptr };
- posix_spawn(&child, launcher_handler.details().executable.characters(), &spawn_actions, &spawn_attributes, const_cast<char**>(argv), environ);
- if (disown(child) < 0)
+ errno = posix_spawn(&child, launcher_handler.details().executable.characters(), &spawn_actions, &spawn_attributes, const_cast<char**>(argv), environ);
+ if (errno) {
+ perror("posix_spawn");
+ } else if (disown(child) < 0) {
  perror("disown");
-
+ }
  posix_spawn_file_actions_destroy(&spawn_actions);
  } else {
  for (auto& path : selected_file_paths()) {
  char const* argv[] = { launcher_handler.details().name.characters(), path.characters(), nullptr };
- posix_spawn(&child, launcher_handler.details().executable.characters(), nullptr, &spawn_attributes, const_cast<char**>(argv), environ);
+ if ((errno = posix_spawn(&child, launcher_handler.details().executable.characters(), nullptr, &spawn_attributes, const_cast<char**>(argv), environ)))
+ continue;
  if (disown(child) < 0)
  perror("disown");
  }