[webrtc-pc] RTCConfiguration.iceServers with undefined?

fippo has just created a new issue for https://github.com/w3c/webrtc-pc:

== RTCConfiguration.iceServers with undefined? ==
a question that came up while writing tests ('cause branch coverage)

How does the [setConfiguration algorithm]( https://w3c.github.io/webrtc-pc/archives/20170515/webrtc.html#dom-rtcpeerconnection-setconfiguration)
> If configuration.iceServers is defined, then run the following steps for each element:
> Let server be the current list element.

deal with this:
```
new RTCPeerConnection({iceServers: [undefined]})
```

Chrome throws a TypeError (Failed to construct 'RTCPeerConnection': Malformed RTCIceServer).
Firefox throws a InvalidAccessError (RTCPeerConnection constructor passed invalid RTCConfiguration - missing urls). Lookig for urls seems like the way to go.

nit: configuration.iceServers must be defined and an array?

Please view or discuss this issue at https://github.com/w3c/webrtc-pc/issues/1251 using your GitHub account