Latin Extended Additional characters in author name blank out citations

[moefuerst]

Bug reports:

A citation is rendered blank if Latin Extended Additional characters are used in the author (family) name.

• Possibly related to https://github.com/seboettg/citeproc-php/issues/143 ?

Used CSL stylesheet:

Tested with: apa-6th-edition.csl, apa.csl, acm-siggraph.csl

Used CSL metadata

[
    {
        "author": [
            {
                "family": "Nguyễn", 
                "given": "Hải"
            },
           {
               "family": "Brown", 
               "given": "John"
           }
        ], 
        "id": "ITEM-2", 
        "type": "book",
        "title": "Two authors writing a book"
    }
]

Expected: Nguyễn, H, Brown, J. Two authors writing a book.

Actual: