[BeckyEbook]

I admit that I also like the native system window, so I played around with simple filtering and in Windows it works.

I know that `QFileDialog::DontUseNativeDialog` is safer, but let's be honest: how many people are going to type in the graphics link instead of pointing to the appropriate file from disk?

Such code works for me.
So I leave the condition only Q_OS_MAC and check the beginning of the path. If http/https then I display a message, but with no crash.

    QFileDialog::Options options = QFileDialog::Options();
#if defined(Q_OS_MAC)
    options = options | QFileDialog::DontUseNativeDialog;
#endif

    // tempfilepaths are full absolute file paths to the files to be added
    QStringList tempfilepaths = QFileDialog::getOpenFileNames(this,
        tr("Add Existing Files"),
        m_LastFolderOpen,
        filter_string,
        NULL,
        options);

    QStringList filepaths;
    for (const QString &path : tempfilepaths) {
    if (path.startsWith("http://", Qt::CaseInsensitive)
     || path.startsWith("https://", Qt::CaseInsensitive)) {
        Utility::DisplayStdErrorDialog(
            tr("The path \"%1\" is not a local file and was not added.").arg(path));
        continue;
    }
        filepaths << path;
    }

Such a preliminary check of the existence of links should be enough, and Windows users will not turn their noses up at the default Qt window.