Protect CEL from an invalid config on reload

This patch fixes CEL to properly handle an invalid config on reload.

(closes issue ASTERISK-22259)
Reported by: Corey Farrell
Tested by: Corey Farrell
Patches:
    cel-config.patch uploaded by Corey Farrell
........

Merged revisions 397033 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@397034 f38db490-d61c-443f-a65b-d21fe96a405b