Description:
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A call to DOMDocument::load() or ::loadXML() in recovery mode leads to segmentation fault in dom_document_parser) when the XML declaration contains an unknown (and unrecoverable) encoding.

The segfault occurs in document.c +1690 when trying to access properties of the result document (ret), which is NULL in this case:

  if (ret->URL == NULL && ctxt->directory != NULL) {

Reproduce code:
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<?php
$xml = '<?xml version="1.0" encoding="bad"?>';
$dom = new DOMDocument;
$dom->recover = true;
$dom->loadXML($xml);
echo $dom->saveXML();

Expected result:
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<?xml version="1.0"?>

Actual result:
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Segmentation Fault