core_local: Fix LocalOptimizationBegin AMI event missing Source channel snapshot.

* Fix the LocalOptimizationBegin AMI event by eliminating an artificial
buffer size limitation that is too small anyway.
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Merged revisions 398572 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@398574 65c4cc65-6c06-0410-ace0-fbb531ad65f3