Add delay before processing FS changes

This prevents file renaming errors in monitored folder on linux, for
example: ABC.torrent.part -> ABC.torrent

src/base/filesystemwatcher.cpp

@@ -124,7 +124,7 @@ void FileSystemWatcher::removePath(const QString &path)
 
 void FileSystemWatcher::scanLocalFolder(const QString &path)
 {
-    processTorrentsInDir(path);
+    QTimer::singleShot(2000, this, [this, path]() { processTorrentsInDir(path); });
 }
 
 #ifndef Q_OS_WIN