Fixed an if check callbook result

application/models/Logbook_model.php

@@ -4131,12 +4131,10 @@ function check_if_callsign_worked_in_logbook($callsign, $StationLocationsArray =
                     $this->session->set_userdata('qrz_session_key', $qrz_session_key);
                 }
 
-
-
                 $callbook = $this->qrz->search($callsign, $this->session->userdata('qrz_session_key'), $use_fullname);
 
                 // if we got nothing, it's probably because our session key is invalid, try again
-                if (!isset($callbook['callsign']))
+                if (($callbook['callsign'] ?? '') == '')
                 {
                     $qrz_session_key = $this->qrz->session($this->config->item('qrz_username'), $this->config->item('qrz_password'));
                     $this->session->set_userdata('qrz_session_key', $qrz_session_key);