res_pjsip_outbound_registration: Ensure URI validation happens in a pjlib thread.

This change moves outbound registration URI validation into the task executed
within a pjlib thread.

Reported by: Andrew Nagy
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Merged revisions 404725 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@404726 f38db490-d61c-443f-a65b-d21fe96a405b
res_pjsip: Ensure more URI validation happens in pj threads.
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Merged revisions 404737 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@404738 f38db490-d61c-443f-a65b-d21fe96a405b