Fix a bot-breaking memory leak from early returning in ParseMediaDescription.
Fix a bot-breaking memory leak from early returning in ParseMediaDescription.

BUG=3791
R=henrike@webrtc.org, pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/22589004

Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 0e52772aa9d3dea65e2cd30187c4ff8e86f9eee4

sippet/talk,sippet/talk,sippet/talk,sippet/talk,sippet/talk