src/main: make using a qapplication use org.kde.breeze not desktop

This fixes QApplication causing org.kde.desktop to be used. This theme
is broken and ugly since everything was built to support org.kde.breeze.
This checks if org.kde.desktop is set, then sets the style to
org.kde.breeze with desktop as the fallback.

Author: ripose-jp

src/main.cpp

@@ -306,6 +306,13 @@ int main(int argc, char *argv[])
 
 #if defined(Q_OS_MACOS) || defined(Q_OS_WIN)
     QQuickStyle::setStyle(QStringLiteral("FluentWinUI3"));
+#else
+    /* Try to avoid overriding the default theme unless it's org.kde.desktop */
+    if (QQuickStyle::name() == "org.kde.desktop")
+    {
+        QQuickStyle::setStyle(QStringLiteral("org.kde.breeze"));
+        QQuickStyle::setFallbackStyle(QStringLiteral("org.kde.desktop"));
+    }
 #endif // defined(Q_OS_MACOS) || defined(Q_OS_WIN)
 
     QQmlApplicationEngine engine;