PHP8 catch ValueError for loadHTML() (#673)
PHP8 catch ValueError for loadHTML() (#673)

Fix
```
PHP Fatal error:  Uncaught ValueError: DOMDocument::loadHTML(): Argument #1 ($source) must not be empty in /SimplePie/Locator.php:83
```

`set_error_handler` does not catch ValueError in PHP8
The code is compatible PHP5 and PHP7.

Fix downstream bug https://github.com/FreshRSS/FreshRSS/issues/3537
Downstream PR https://github.com/FreshRSS/FreshRSS/pull/3547
mblaney/simplepie,simplepie/simplepie,mblaney/simplepie,FreshRSS/simplepie,simplepie/simplepie,FreshRSS/simplepie