func_curl: Fix leak of an ast_str in error handling code path.

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Merged revisions 360413 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 360414 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@360415 65c4cc65-6c06-0410-ace0-fbb531ad65f3