Prevent asserting on unset start bitrate.
Prevent asserting on unset start bitrate.

Quick fix for crash in WebRtcBrowserTest.NegotiateOfferWithBLine.
Follow-up CL from stefan@ that changes this path is under review.

BUG=1788,1667
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/51419005

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#8823}
git-svn-id: 917f5d3ca488f358c4d40eaec14422cf392ccec9@8823 4adac7df-926f-26a2-2b94-8c16560cd09d

TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc