bug#53334: qbittorrent(<=4.4.0)'s search window fails with "Python is required to use the search engine but it does not seem to be installed"

[Jacob Hrbek]

qbittorrent <=4.4.0 (current latest version) fails with:

```
Missing Python Runtime

Python is required to use the search engine but it does not seem to be installed
```

which is triggered from `qbittorrent/src/gui/mainwindow.cpp`:

```cpp

/* https://github.com/qbittorrent/qBittorrent/blob/00f6bb7c8225285a7929426187a1513d247b582b/src/gui/mainwindow.cpp#L1847 */
void MainWindow::on_actionSearchWidget_triggered()
{
    if (!m_hasPython && m_ui->actionSearchWidget->isChecked())
    {
        const Utils::ForeignApps::PythonInfo pyInfo = Utils::ForeignApps::pythonI
nfo();

        // Not installed
        if (!pyInfo.isValid())
        {
            m_ui->actionSearchWidget->setChecked(false);
            Preferences::instance()->setSearchEnabled(false);

#ifdef Q_OS_WIN
            const QMessageBox::StandardButton buttonPressed = QMessageBox::question(this, tr("Missing Python Runtime")
                , tr("Python is required to use the search engine but it does not seem to be installed.\nDo you want to install it now?")
                , (QMessageBox::Yes | QMessageBox::No), QMessageBox::Yes);
            if (buttonPressed == QMessageBox::Yes)
                installPython();
#else
            QMessageBox::information(this, tr("Missing Python Runtime")
                , tr("Python is required to use the search engine but it does not seem to be installed."));
#endif
            return;
        }

        // Check version requirement
        if (!pyInfo.isSupportedVersion())
        {
            m_ui->
;actionSearchWidget->setChecked(false);
            Preferences::instance()->setSearchEnabled(false);

#ifdef Q_OS_WIN
            const QMessageBox::StandardButton buttonPressed = QMessageBox::question(this, tr("Old Python Runtime")
                , tr("Your Python version (%1) is outdated. Minimum requirement: %2.\nDo you want to install a newer version now?")
                    .arg(pyInfo.version, QLatin1String("3.5.0"))
                , (QMessageBox::Yes | QMessageBox::No), QMessageBox::Yes);
            if (buttonPressed == QMessageBox::Yes)
                installPython();
#else
            QMessageBox::information(this, tr("Old Python Runtime")
                , tr("Your Python version (%1) is outdated. Please upgrade to latest version for search engines to work.\nMinimum requirement: %2.")
                .arg(pyInfo.version, QLatin1String("3.5.0")));
#endif
            return;
        }

        m_hasPython = true;

    m_ui->actionSearchWidget->setChecked(true);
        Preferences::instance()->setSearchEnabled(true);
    }

    displaySearchTab(m_ui->actionSearchWidget->isChecked());
}
```

To call `Utils::ForeignApps::pythonInfo()` definition in `qbittorrent/src/base/utils/foreignapps.cpp` as:

```cpp

/* https://github.com/qbittorrent/qBittorrent/blob/5c0378a6845e3484023f4c76893ff9f0e5178460/src/base/utils/foreignapps.cpp#L272 */
PythonInfo Utils::ForeignApps::pythonInfo()
{
    static PythonInfo pyInfo;
    if (!pyInfo.isValid())
    {
        if (testPythonInstallation("python3", pyInfo))
            return pyInfo;

        if (testPythonInstallation("python", pyInfo))
            return pyInfo;

#if defined(Q_OS_WIN)
        if (tes
tPythonInstallation(findPythonPath(), pyInfo))
            return pyInfo;
#endif

        LogMsg(QCoreApplication::translate("Utils::ForeignApps", "Python not detected"), Log::INFO);
    }

    return pyInfo;
}
```

Where:

```cpp
if (testPythonInstallation("python3", pyInfo)) ...
```

Is important as it's checking for a `python3` (or `python`) executable in PATH that is not provided by guix's build procedure -> The package has compatibility issues with GNU Guix and has to be patched.


### Steps to reproduce:
0. Get qbittorrent on GNU Guix
1. Open the GUI: View > Search engine and observe the highlighted error preventing to use the search engine functionality

Relevants:
R1. https://github.com/qbittorrent/qBittorrent/issues/16139

--
Jacob Hrbek

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