cannot get min/avg/max when stddev is nan

[elixiao]

Example:

$ ping -c 1 taobao.com
PING www.taobao.com.danuoyi.tbcache.com (122.225.217.183): 56 data bytes
64 bytes from 122.225.217.183: icmp_seq=0 ttl=53 kj=4.628 ms

--- www.taobao.com.danuoyi.tbcache.com ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 4.628/4.628/4.628/nan ms

Parsed result is:

{
  inputHost: "www.taobao.com",
  host: "www.taobao.com.danuoyi.tbcache.com",
  alive: true,
  output:
    "PING www.taobao.com.danuoyi.tbcache.com (122.225.217.183): 56 data bytes\n64 bytes from 122.225.217.183: icmp_seq=0 ttl=53 kj=4.628 ms\n\n--- www.taobao.com.danuoyi.tbcache.com ping statistics ---\n1 packets transmitted, 1 packets received, 0.0% packet loss\nround-trip min/avg/max/stddev = 4.628/4.628/4.628/nan ms\n",
  time: 4.628,
  times: [4.628],
  min: "unknown",
  max: "unknown",
  avg: "unknown",
  stddev: "NaN",
  packetLoss: "0.000",
  numeric_host: "122.225.217.183",
}

actually min/max/avg is 4.628, but got unknown.