Idea for fix issue #264

[arkanoider]

Hi @grunch ,

first idea for fix the issue #264 .

Modified a bit this function pubkey_event_can_solve

pub async fn pubkey_event_can_solve(
    pool: &Pool<Sqlite>,
    ev_pubkey: &PublicKey,
    status: Status,
) -> bool {
    if let Ok(my_keys) = crate::util::get_keys() {
        // Is mostro admin taking dispute?
        if ev_pubkey.to_string() == my_keys.public_key().to_string()
            && matches!(status, Status::InProgress | Status::Initiated)
        {
            return true;
        }
    }

    // Is a solver taking a dispute
    if let Ok(solver) = find_solver_pubkey(pool, ev_pubkey.to_string()).await {
        if solver.is_solver != 0_i64 && status == Status::Initiated {
            return true;
        }
    }

    false
}

In this way if a solver takes first a dispute we have to check that dispute is in Initiated state, which (imo) is the only one a solver can take.
While an admin can overtake also InProgress state, so now he will become the solver and other solvers cannot take the dispute again.

You will see that I removed also pubkey_event_can_solve from admin_cancel.rs and admin_settle.rs because ( still imo ) they are redundat because of is_assigned_solver that is responsible to check if the pubkey of message is the solver.
If, for example, an admin overtake a solver dispute he will be the new solver so the check below should be enough.

   match is_assigned_solver(pool, &event.pubkey.to_string(), order_id).await {
        Ok(false) => {
            send_cant_do_msg(
                None,
                Some("Dispute not taken by you".to_string()),
                &event.pubkey,
            )
            .await;

            return Ok(());
        }
        Err(e) => {
            error!("Error checking if solver is assigned to order: {:?}", e);
            return Ok(());
        }
        _ => {}
    }

Let me know!

[grunch]

LGTM