PHP warning on non-character entries

[rxu]

In rare cases when text contains some non-character symbols, PHP warning is thrown, f.e.:

[phpBB Debug] PHP Warning: in file [ROOT]/vendor/s9e/text-formatter/src/Utils.php on line 161: DOMDocument::loadXML(): PCDATA invalid Char value 65534 in Entity, line: 36

or

Warning: DOMDocument::loadXML(): Char 0xFFFE out of allowed range in Entity, line: 8 in /home/mydomain/cableold/phpbb3/vendor/s9e/text-formatter/src/Utils.php on line 161
PHP Warning: DOMDocument::loadXML(): PCDATA invalid Char value 65534 in Entity, line: 8 in /home/mydomain/cableold/phpbb3/vendor/s9e/text-formatter/src/Utils.php on line 161

Example reports:
https://www.phpbb.com/community/viewtopic.php?t=2656027
https://www.phpbb.com/community/viewtopic.php?t=2651761
Recent report in phpBB Discord support channel: https://discord.com/channels/220192692573962241/508793734842941480/1444785568054509578

That may happen while handling entries like f.e. 0xFFFE or 0xFFFF.

It seems that is shouldn't generate PHP errors though if handled/escaped somehow by the library.