MDL-65375 Restore: Null data in other field should be serialised

If the 'other' field is empty, then following a restore of course
logs, it should still be serialised so that it is consistent with
the normal behaviour when logging.

Without this change, an event with null value for other has the
field set to NULL if you restore it, but 'N;' when the event is
initially created.

admin/tool/log/backup/moodle2/restore_tool_log_logstore_subplugin.class.php

@@ -137,14 +137,14 @@ abstract class restore_tool_log_logstore_subplugin extends restore_subplugin {
                         }
                     }
                 }
-                // Now we want to serialize it so we can store it in the DB.
-                $data->other = serialize($data->other);
             } else {
                 $message = "Event class not found: \"$eventclass\". Skipping log record.";
                 $this->log($message, backup::LOG_DEBUG);
                 return; // No such class, can not restore.
             }
         }
+        // Now we want to serialize it so we can store it in the DB.
+        $data->other = serialize($data->other);
 
         return $data;
     }