A crash would occur when the router tried to match an
against an empty address pattern array.

The following configuration was used to reproduce the
issue:

{
    "listeners": {
        "127.0.0.1:8082": {
            "pass": "routes"
        }
    },
    "routes": [
        {
            "match": {
                "source": []
            },
            "action": {
                "return": 200
            }
        }
    ]
}

In the case that routes or upstreams is empty and the pass option is a variable.
If the resolved pass is routes or upstreams, a segment error occurred.

When processing a restart request, the router sends a QUIT message to all
existing processes of the application.  Then, a new shared application port is
created to ensure that new requests won't be handled by the old processes of
the application.

This commit fixes a rare crash that can occur when File.write is
called by many threads.