### Preflight Checklist
* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### Issue Details
```js
let ret = shell.openItem('file:///noexistent');
console.log(ret);
```
`ret` is always `true` on Linux even if opening fails, e.g.
```sh
xdg-open 'file:///noexistent'
echo $?
```
Shows nonzero error code.

* **Electron Version:**
  * v6.0.11
* **Operating System:**
  *Linux / Ubuntu 16.04 x64

### Expected Behavior
`ret` should be `false`, if `xdg-open` returns non-zero code.

Optional: It would be very nice if the `xdg-open` error (catch stderr) would be displayed in `dialog.showErrorBox` if it returns non-zero code. Just take care that `xdg-open` may write some warnings to stderr even if it returns 0.

shell/common/api/atom_api_shell.cc
const base::FilePath& path) {
  using base::win::ShortcutProperties;
  gin::Dictionary options = gin::Dictionary::CreateEmpty(thrower.isolate());
  base::win::ScopedCOMInitializer com_initializer;
  base::win::ShortcutProperties properties;
  if (!base::win::ResolveShortcutProperties(
          path, ShortcutProperties::PROPERTIES_ALL, &properties)) {
    thrower.ThrowError("Failed to read shortcut link");
    return v8::Null(thrower.isolate());
  }
  options.Set("target", properties.target);
  options.Set("cwd", properties.working_dir);
  options.Set("args", properties.arguments);
  options.Set("description", properties.description);
  options.Set("icon", properties.icon);
  options.Set("iconIndex", properties.icon_index);
  options.Set("appUserModelId", properties.app_id);
  return gin::ConvertToV8(thrower.isolate(), options);
}
#endif
void Initialize(v8::Local<v8::Object> exports,