bt_le_adv_stop null pointer exception

[JoeEtacompute]

Describe the bug
In subsys/bluetooth/host/adv.c .Move null pointer check to before calling bt_le_lim_adv_cancel_timeout.

Original Code

int bt_le_adv_stop(void)
{
        struct bt_le_ext_adv *adv = bt_le_adv_lookup_legacy();
        int err;

        (void)bt_le_lim_adv_cancel_timeout(adv);

        if (!adv) {
                BT_ERR("No valid legacy adv");
                return 0;
        }

Suggested modification:

int bt_le_adv_stop(void)
{
        struct bt_le_ext_adv *adv = bt_le_adv_lookup_legacy();
        int err;

       if (!adv) {
                BT_ERR("No valid legacy adv");
                return 0;
        }
        (void)bt_le_lim_adv_cancel_timeout(adv);
}

[carlescufi]

@JoeEtacompute thanks for the report. Would you mind opening a Pull Request with your suggested change?