Resolve a crash in res_smdi when used with chan_dahdi.

Resolve a crash in res_smdi when used with chan_dahdi.

When chan_dahdi goes to get an SMDI message, it provides no search criteria.
It just grabs the next message that arrives.  This code was written with the
SMDI dialplan functions in mind, since that is now the preferred method of
using SMDI.  However, this broke support of it being used from chan_dahdi.

(closes AST-212)

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@190661 65c4cc65-6c06-0410-ace0-fbb531ad65f3