PdfIndexer is not able to handle array of keywords

[andre-spindler]

The pdf indexer fails if the file contains an array of keywords in the pdf metadata block.
In this cails the scheduler task fails and an entry to the typo3 log is written. Every index run.
The error occurs when the values of the metadata block are parsed and converted to xml.
This should be improved to handle single values and also arrays.
The second image shows the array $pdf->properties.

TYPO3: 10.4.17
PHP: 7.4.20
EXT:metadata: 4.0.0