Bugs for stopped pm2 items

In `pm2/__init__.py` Line 68-73: 
```python
    def __init__(self, json_data: dict) -> None:
        self.name = json_data["name"]
        if json_data["pid"]:
            self.pid = json_data["pid"]
        if json_data["pm_id"]:
            self.pm_id = json_data["pm_id"]
```

When pm2 has some stopped items those have no pids, `if json_data["pid"]` report bugs!