Bluetooth: Audio: Add conn check for CSIS client notify handlers
Bluetooth: Audio: Add conn check for CSIS client notify handlers

Add a NULL check for the conn pointer in the CSIS client
notify handlers.

Signed-off-by: Emil Gydesen <a20314356615223738233ab4c4eb1cd8cd4146fa@nordicsemi.no>

zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr