net: lwm2m: fix potential invalid pointer dereference in reset message
net: lwm2m: fix potential invalid pointer dereference in reset message

Sometimes message is being reset from multiple locations in code.
If message has already been reset, pointer to context is invalid.

Signed-off-by: Marin Jurjević <b0cd402275f93db923f965efd471b503030e79b6@hotmail.com>

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