Prevent crashes in res_config_odbc due to uninitialized string fields.

Patches:
    odbc-crash.patch by John Hardin (License #6512)
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Merged revisions 413241 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 413251 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 413258 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@413263 f38db490-d61c-443f-a65b-d21fe96a405b
Blocked revisions 413282

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Correct variable traversal logic in res_config_odbc's update_odbc function.

Closes issue ASTERISK-23675
Reported by Leando Dardini
Patches:
	asterisk-23675-odbc-linkedlist-traversal_12.diff uploaded by Michael L. Young (license #5026)


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@413283 f38db490-d61c-443f-a65b-d21fe96a405b