Fix #455 force recheck on completed torrents causing crash

libtorrent/src/torrent.cpp

@@ -667,6 +667,7 @@ namespace libtorrent
 			, m_save_path, m_ses.m_files, m_ses.m_disk_thread, m_storage_constructor
 			, m_storage_mode);
 		m_storage = m_owning_storage.get();
+		if (!m_picker) m_picker.reset(new piece_picker());
 		m_picker->init(m_torrent_file->piece_length() / m_block_size
 			, int((m_torrent_file->total_size()+m_block_size-1)/m_block_size));
 		// assume that we don't have anything