dult: Move assert after ready check in ANOS characteristic handler

Moved assert after the subsys ready check in the ANOS GATT
characteristic write handler as the pointer checked in the assert
is initialized on the dult_enable call.
It could result in assertion when the DULT was not yet initialized
but characteristic was accessed as it is statically defined.
Now instead of assertion it just gracefully returns from the function.

Jira: NCSDK-33739

Signed-off-by: Mateusz Kapala <[email protected]>

Author: mkapala-nordic

doc/nrf/releases_and_maturity/releases/release-notes-changelog.rst

@@ -554,7 +554,9 @@ nRF RPC libraries
 Other libraries
 ---------------
 
-|no_changes_yet_note|
+* :ref:`dult_readme` library:
+
+  * Updated the write handler of the accessory non-owner service (ANOS) GATT characteristic to no longer assert on write operations if the DULT was not enabled at least once.
 
 Shell libraries
 ---------------

subsys/dult/bt/anos.c

@@ -519,18 +519,18 @@ static ssize_t write_accessory_non_owner(struct bt_conn *conn,
 	const struct dult_user *dult_user;
 	enum dult_near_owner_state_mode mode;
 
-	/* The Accessory Non-owner characteristic should be used to handle the GATT Write
-	 * operations and to send GATT indications.
-	 */
-	__ASSERT_NO_MSG(attr == anos_chrc_indicate_attr);
-
 	if (!dult_user_is_ready()) {
 		res = BT_GATT_ERR(BT_ATT_ERR_UNLIKELY);
 		LOG_INF("Accessory non-owner write: res=%d conn=%p, "
 			"Return error because DULT is not enabled", res, (void *)conn);
 		return res;
 	}
 
+	/* The Accessory Non-owner characteristic should be used to handle the GATT Write
+	 * operations and to send GATT indications.
+	 */
+	__ASSERT_NO_MSG(attr == anos_chrc_indicate_attr);
+
 	if (offset != 0) {
 		LOG_WRN("Invalid offset: off=%" PRIu16 " (Accessory non-owner write)", offset);
 		res = BT_GATT_ERR(BT_ATT_ERR_INVALID_OFFSET);