When investigating another bug reported by GitHub user 'tstangner',
I discovered that PHP segfaults when the INI parameter
zend.script_encoding is set to "pass". This bug dates back to
December 2022 (caused by yours truly in 953864661a).
If any PHP users in the wild were actually setting zend.script_encoding
to "pass" (which would be an utterly useless thing to do), I expect that
someone would have filed a bug report by now. The absence of such bug
reports is evidence that nobody is doing this.
Hence, it seems that the best fix is simply to disallow "pass" as a
choice for zend.script_encoding. The internal function
'php_mb_zend_encoding_list_parser' which I am modifying to accomplish
this has no other in-tree callers, aside from the 'exif' extension.
Further, exif only calls the function with a few hard-coded values, and
none of them are the string "pass", so this change will not have any
impact on exif.
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