FsDiscoverer: Fix unneeded blacklist copy

src/discoverer/FsDiscoverer.cpp

@@ -126,7 +126,7 @@ void FsDiscoverer::checkDevices()
     }
 }
 
-void FsDiscoverer::checkFolder( fs::IDirectory& currentFolderFs, Folder& currentFolder, const std::vector<std::shared_ptr<Folder>> blacklist ) const
+void FsDiscoverer::checkFolder( fs::IDirectory& currentFolderFs, Folder& currentFolder, const std::vector<std::shared_ptr<Folder>>& blacklist ) const
 {
     // We already know of this folder, though it may now contain a .nomedia file.
     // In this case, simply delete the folder.

src/discoverer/FsDiscoverer.h

@@ -44,7 +44,7 @@ private:
     /// \brief checkSubfolders
     /// \return true if files in this folder needs to be listed, false otherwise
     ///
-    void checkFolder( fs::IDirectory& currentFolderFs, Folder& currentFolder, const std::vector<std::shared_ptr<Folder>> blacklist ) const;
+    void checkFolder( fs::IDirectory& currentFolderFs, Folder& currentFolder, const std::vector<std::shared_ptr<Folder>>& blacklist ) const;
     void checkFiles(fs::IDirectory& parentFolderFs, Folder& parentFolder ) const;
     std::vector<std::shared_ptr<Folder>> blacklist() const;
     bool isBlacklisted( const fs::IDirectory& directory, const std::vector<std::shared_ptr<Folder>>& blacklist ) const;