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 v5.4.156 by commit 285e9210b1fab96a11c0be3ed5cea9dd48b6ac54. For more details please see the references link.