Fix segmentation fault when PDUSession Release

The if below checks if pduSession is NULL, but inside the if there is pduSession->xid = xid; where we try to set xid to a NULL variable.

 if (!pduSession) {
      LOG_I(NR_RRC, "no pdusession_id, AMF requested to close it id=%d\n", cmd->pdusession_release_params[pdusession].pdusession_id);
      int j=UE->nb_of_pdusessions++;
      UE->pduSession[j].status = PDU_SESSION_STATUS_FAILED;
      UE->pduSession[j].param.pdusession_id = cmd->pdusession_release_params[pdusession].pdusession_id;
      UE->pduSession[j].cause = NGAP_CAUSE_RADIO_NETWORK;
      UE->pduSession[j].cause_value = 30;
      pduSession->xid = xid;
      continue;
    }

By removing the line, we can set mobile phones (Pixel 7) to airplane mode without getting segmentation fault at the gNB.