Disable update checks on versions before Windows 10

On versions before Windows 10 the user is running the Qt5 build.
The next qBittorrent release will change to Qt6 as the default build.
It is counterintuitive to tell the user about available updates when they are
running an incompatible Windows version.

src/gui/mainwindow.cpp

@@ -31,6 +31,11 @@
 #include <algorithm>
 #include <chrono>
 
+#if defined(Q_OS_WIN)
+#include <Windows.h>
+#include <versionhelpers.h>  // must follow after Windows.h
+#endif
+
 #include <QActionGroup>
 #include <QClipboard>
 #include <QCloseEvent>
@@ -273,9 +278,15 @@ MainWindow::MainWindow(IGUIApplication *app, const State initialState)
 #if defined(Q_OS_WIN) || defined(Q_OS_MACOS)
     connect(m_ui->actionCheckForUpdates, &QAction::triggered, this, [this]() { checkProgramUpdate(true); });
 
+#ifdef Q_OS_WIN
+    if (::IsWindows10OrGreater() && pref->isUpdateCheckEnabled())
+        checkProgramUpdate(false);
+#else
+
     // trigger an early check on startup
     if (pref->isUpdateCheckEnabled())
         checkProgramUpdate(false);
+#endif
 #else
     m_ui->actionCheckForUpdates->setVisible(false);
 #endif
@@ -1483,7 +1494,11 @@ void MainWindow::loadPreferences()
 #if defined(Q_OS_WIN) || defined(Q_OS_MACOS)
     if (pref->isUpdateCheckEnabled())
     {
+#ifdef Q_OS_WIN
+        if (::IsWindows10OrGreater() && !m_programUpdateTimer)
+#else
         if (!m_programUpdateTimer)
+#endif
         {
             m_programUpdateTimer = new QTimer(this);
             m_programUpdateTimer->setInterval(24h);
@@ -1919,6 +1934,21 @@ void MainWindow::updatePowerManagementState()
 #if defined(Q_OS_WIN) || defined(Q_OS_MACOS)
 void MainWindow::checkProgramUpdate(const bool invokedByUser)
 {
+#ifdef Q_OS_WIN
+    if (!::IsWindows10OrGreater())
+    {
+        if (invokedByUser) {
+            auto *msgBox = new QMessageBox {QMessageBox::Information, u"qBittorrent"_qs
+                                           , tr("This is the last supported version for your Windows version.")
+                                           , QMessageBox::Ok, this};
+            msgBox->setAttribute(Qt::WA_DeleteOnClose);
+            msgBox->show();
+        }
+
+        return;
+    }
+#endif
+
     if (m_programUpdateTimer)
         m_programUpdateTimer->stop();