Fix crashes in res_odbc.

The variable "class" was being set NULL just prior to
being dereferenced in an ao2_link call. I have moved
the setting of the variable to NULL until after the
ao2_link call.



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@165724 65c4cc65-6c06-0410-ace0-fbb531ad65f3