Don't crash if createDataChannel fails.
Don't crash if createDataChannel fails.

It can fail in some real circumstances, such as when IDs are exhausted
or you explicitly try to create one with an already-used ID.

Review-Url: https://codereview.webrtc.org/2181933002
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#13535}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 5f5504f218080e83e1eb64ce139535e5678ede16

Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk