isdn: cpai: check ctr->cnr to avoid array index out of bound
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v4.4.290 by commit e8b8de17e164c9f1b7777f1c6f99d05539000036. For more details please see the references link.