Don't try to parse empty Ice urls.

https://crrev.com/7c4e7458b5ce99c13a75d5be7d718ef94e2f8f9f added support
to pass a list of urls for IceServer configurations. This CL fixes a
potential crash when empty urls are passed.

BUG=2096
R=tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/51969004

Cr-Commit-Position: refs/heads/master@{#9334}
2 files changed