Comment 1 for bug 2025061

I encountered this when trying to reweight some already-generated events with `./bin/madevent reweight run_01` inside the output directory. I can paste a full reproducer here if the above case is not enough.

To try investigating myself, I added some printouts on line 687 of common_run_interface, and found that MADEVENT is False so it never picks up the `root_path` which for me was set seemingly correctly `/usr/local/venv/MG5_aMC`