Resolve more memory leaks in xmldoc

Many places that allocated to pull out an attribute are now freed
properly.


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@382600 f38db490-d61c-443f-a65b-d21fe96a405b
Fix a memory leak in xmldoc

Another instance of attribute retrieval not being freed properly.


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@382604 f38db490-d61c-443f-a65b-d21fe96a405b