[Yii2] Fixed unintentional DB connection drop during exception logging

[ivokund]

Fixes #3696

[samdark]

That's super-weird. Why can't vardumper deal with it?

[samdark]

But otherwise it looks like it doesn't break anything so @DavertMik, let's merge it.

[DavertMik]

@samdark that's why #3696 (comment)

please review, maybe there is a nicer way to overcome this error.

[samdark]

I see no better solution.

[DavertMik]

Thanks

[ivokund]

@samdark @DavertMik This is actually a simplified proof of concept of one way to close DB connection in Yii2 :)

        $func = function () { 
            throw new \Exception();
        };

        try {
            $func(\Yii::$app->db);
        } catch (\Exception $e) {
            \yii\helpers\VarDumper::export($e);
        }

\Yii::$app->db is present in Exception's trace and thus gets serialized in BaseVarDumper.php:197, which in turn calls __sleep and close in \yii\db\Connection.

This will probably pop up elsewhere as well and needs a proper fix at some point. My first guess would be that \yii\helpers\BaseVarDumper::exportInternal needs a special case handling exceptions that calls __toString() on the Exception rather than tries to serialize it.