checkForUSBStick(): look for etc/psa_config in mountpath-directory.

common/src/System.cpp

@@ -251,8 +251,7 @@ bool System::test_dir(const QString& dir)
 
 
 
-bool System::checkForUSBStick()
-{
+std::optional<QString> System::checkForUSBStick(QString const &dirPathUnderMountPath) {
 #if defined (ARCH_DesktopLinux)
     // DEBUG / TEST:
     if (QFileInfo(getUSBMountPath()).isDir())
@@ -261,11 +260,9 @@ bool System::checkForUSBStick()
         return false;
 #endif
 
-    if (getUSBMountPath().isEmpty()) {
-        return false;
-    }
-
-    return true;
+    QString const &mountPath = getUSBMountPath(dirPathUnderMountPath);
+    // qCritical() << "MOUNT-PATH" << mountPath;
+    return mountPath.isEmpty() ? std::nullopt : std::optional<QString>(mountPath);
 }