res_pjsip: Fix memory leak of nameservers in off-nominal resolver creation failure.

Thanks Walter Doekes!
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Merged revisions 410844 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@410845 f38db490-d61c-443f-a65b-d21fe96a405b