owr_transport: plug PendingSessionInfo leak
owr_transport: plug PendingSessionInfo leak

Closes #630.

pererikb/openwebrtc,EricssonResearch/openwebrtc,shoreflyer/openwebrtc,pererikb/openwebrtc,EricssonResearch/openwebrtc,pererikb/openwebrtc,shoreflyer/openwebrtc,pererikb/openwebrtc,EricssonResearch/openwebrtc,shoreflyer/openwebrtc,shoreflyer/openwebrtc,shoreflyer/openwebrtc,pererikb/openwebrtc,pererikb/openwebrtc,EricssonResearch/openwebrtc,pererikb/openwebrtc,EricssonResearch/openwebrtc,EricssonResearch/openwebrtc,EricssonResearch/openwebrtc,shoreflyer/openwebrtc,shoreflyer/openwebrtc