Method history_size

plugins/workflow.cpp:312–314

    static const size_t hist_entry_size = PersistentDataItem::int28_size * 4;

    size_t history_size() {
        return history.data_size() / hist_entry_size;
    }
    int history_value(int idx, HistoryItem item) {
        size_t hsize = history_size();
        size_t base = ((history.ival(0)+1+idx) % hsize) * hist_entry_size;