Ensure addItem operation is thread-safe / protected by a mutex #155
Description
Might be related to #80
When migration mwoffliner to libzim 9, we had issues about systematic segfaults when we were adding files in the ZIM creator from multiple threads at the same time.
We had to protect the operation with a mutex, see openzim/mwoffliner@22283a6
This should be fixed or handled at node-libzim level instead of scraper level.