Mysqli driver raise a lot of warning about Undefined property after connection closed

[ralphschindler]

The problem is in the Mysqli\Connection::Disconnect() that unset property but other methods check it and raise warning. So to fix it just add $this->resource=null; in the end of disconnect method:

---

public function disconnect()
{
    if ($this->resource instanceof \mysqli) {
        $this->resource->close();
    }
    unset($this->resource);
    $this->resource=null; // +++ ADD this string
}

---

[ThaDafinser]

@digihand it seems that it's done in every Db\Adapter\Driver* different...
Here it's unset(), mostly it's set to null and sometimes it's only disconnected.

maybe @ralphschindler could have a look into it and apply some labels.

[samsonasik]

@ThaDafinser @digihand maybe the case is like at this PR #5887 ?