AbsoluteUrlReplacer: Ignore mysqli instances

[pavelevap]

Fatal error: ReflectionProperty::setValue(): Cannot write property [...]wp-content/plugins/versionpress/src/Utils/AbsoluteUrlReplacer.php on line 105

Related: versionpress/support#127

Code example to reproduce this error:

<?php
$mysqli = new mysqli();
$reflection = new ReflectionClass(mysqli::class);

$property = $reflection->getProperty('affected_rows');
$property->setAccessible(TRUE);
$property->setValue($mysqli, 10);

It is probably caused by some plugin which stores serialized mysqli instance into WordPress database.