Handle Surrogate channels in Dial message processing

Depending on when a Surrogate channel replaces an existing channel, it is
possible to get a Dial message for the Surrogate channel. When this occurs, no
CDR will exist for the channel as Surrogate channels are ignored. Safely handle
the case when a CDR doesn't exist for a Dial message.


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@396371 f38db490-d61c-443f-a65b-d21fe96a405b