MDL-41266 Logging: Added choose option for external database store

admin/tool/log/store/database/classes/helper.php

@@ -39,6 +39,7 @@ class helper {
      */
     public static function get_drivers() {
         return array(
+            ''               => get_string('choosedots'),
             'native/mysqli'  => \moodle_database::get_driver_instance('mysqli', 'native')->get_name(),
             'native/mariadb' => \moodle_database::get_driver_instance('mariadb', 'native')->get_name(),
             'native/pgsql'   => \moodle_database::get_driver_instance('pgsql', 'native')->get_name(),

admin/tool/log/store/database/classes/log/store.php

@@ -70,7 +70,7 @@ class store implements \tool_log\log\writer, \core\log\sql_select_reader {
         }
 
         $dbdriver = $this->get_config('dbdriver');
-        if (!$dbdriver) {
+        if (empty($dbdriver)) {
             $this->extdb = false;
             return false;
         }