nil pointer on docker master

[vikstrous]

While testing out moby/moby#21840 I ran into this nil pointer exception in libnetwork:

https://gist.github.com/vikstrous/8450cefcbd77739d3ceecb8f33001a2f

[vikstrous]

I'm also running into this in 1.11-rc4

[vikstrous]

update: this seems to be triggered by doing a dns request, then exiting the container before receiving the response