Bluetooth: classic: obex: Fix active client validation logic

Fix the active client validation in OBEX abort operations to
handle concurrent request scenarios. The check now
ensures that if there is an active client and it's different
from the current client, the operation is rejected with -EBUSY.

Signed-off-by: Cheng Chang <cheng.chang@nxp.com>

Author: CC0918

subsys/bluetooth/host/classic/obex.c

@@ -2077,7 +2077,7 @@ int bt_obex_abort(struct bt_obex_client *client, struct net_buf *buf)
 	}
 
 	active_client = atomic_ptr_get(&client->obex->_active_client);
-	if (active_client != client) {
+	if ((active_client != NULL) && (active_client != client)) {
 		LOG_WRN("One OBEX request is executing");
 		return -EBUSY;
 	}