Please fix the bug

[leonqli]

The original code will fail if there is a zombie process.
Correct one: cmdline = " ".join(pinfo.get("cmdline") or [])

https://github.com/ad-freiburg/qlever-control/blob/bd07360654a432216e46770650bf5fb3f978f3c8/src/qlever/util.py#L288