Cannot catch querypath parser errors

### HHVM Version

3.14.0-dev
### Standalone code, or other way to reproduce the problem

```
This is invalid HTML <
HTML;

function errorHandler($errno, $errstr) {
var_dump('handling error', $errno, $errstr);
}

set_error_handler('errorHandler', E_ERROR | E_WARNING | E_USER_ERROR | E_USER_WARNING);

$qp->html($h);
```
### Expected result

In Zend, the error handler gets called 4 times:

```
string(14) "handling error"
int(2)
string(95) "DOMDocumentFragment::appendXML(): Entity: line 1: parser error : StartTag: invalid element name"
string(14) "handling error"
int(2)
string(68) "DOMDocumentFragment::appendXML():

"
string(14) "handling error"
int(2)
string(62) "DOMDocumentFragment::appendXML(): ^"
string(14) "handling error"
int(2)
string(91) "DOMDocumentFragment::appendXML(): Entity: line 1: parser error : chunk is not well balanced"
```
### Actual result

In HHVM, it gets called 0 times:

```
Entity: line 1: parser error : StartTag: invalid element name

^
Entity: line 1: parser error : chunk is not well balanced
```