added reference link to SQL error code

[ci skip]

extensions/sphinx/Schema.php

@@ -455,6 +455,7 @@ class Schema extends Object
             $previous = $e->getPrevious();
             if ($previous instanceof \PDOException && strpos($previous->getMessage(), 'SQLSTATE[42S02') !== false) {
                 // index does not exist
+                // https://dev.mysql.com/doc/refman/5.5/en/error-messages-server.html#error_er_bad_table_error
                 return false;
             }
             throw $e;

framework/db/mysql/Schema.php

@@ -190,6 +190,7 @@ class Schema extends \yii\db\Schema
             $previous = $e->getPrevious();
             if ($previous instanceof \PDOException && strpos($previous->getMessage(), 'SQLSTATE[42S02') !== false) {
                 // table does not exist
+                // https://dev.mysql.com/doc/refman/5.5/en/error-messages-server.html#error_er_bad_table_error
                 return false;
             }
             throw $e;