res_pjsip_notify: Fix crash on unload/load and don't say the module doesn't exist on reload.

When unloading the module did not unregister the CLI commands causing a crash upon
load when they were registered again.

When reloading the module the return value from the config options framework was not
checked to determine if an error occurred or not. This caused a message to be output
saying the module did not exist when reloading if no changes were present.

AST-1433 #close
AST-1434 #close
........

Merged revisions 423579 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/13@423580 f38db490-d61c-443f-a65b-d21fe96a405b