check if db_table_exists for watchdog table

there are several warnings displayed on 'admin/settings/supercron' if drupal`s watchdog module disabled

so, on line 293
just add

if (db_table_exists('watchdog')){

in the end code should look like:

    if (db_table_exists('watchdog')){
      $result = db_query("SELECT * FROM {watchdog} WHERE type='cron exception' ORDER BY wid DESC");
    
      $act = FALSE;
      while ($r = db_fetch_array($result)) {
        $variables = unserialize($r["variables"]);
        if ($variables["@module"]==$row->module_name) {
          $act = TRUE;
          break;
        }
      }
    }