Description:
------------
The checksum can be incorrectly computed when a file to be cached contains non-ascii characters.  When the opcache computes the checksum before it writes the file it chains together two calls to zend_adler32. 

https://github.com/php/php-src/blob/PHP-7.2.24/ext/opcache/zend_file_cache.c#L870

When the bin file containing the opcache is loaded it computes the checksum with a single call to zend_adler32.

https://github.com/php/php-src/blob/PHP-7.2.24/ext/opcache/zend_file_cache.c#L1461

The zend_adler32 function uses signed chars instead of unsigned chars. As a result non-ascii characters can have negative values. This means checksum is incorrectly computed and chained calls can result in different values than a single call to zend_adler32.

https://github.com/php/php-src/blob/PHP-7.2.24/ext/opcache/zend_accelerator_util_funcs.c#L738

Test script:
---------------
Ini settings
opcache.enable=1
opcache.enable_cli=1
opcache.file_cache=/tmp
opcache.log_verbosity_level=3

<?php
$mbChars = ['°','₀','۰','０','¹','₁','۱','１','²','₂','۲','２','³','₃','۳','３','⁴','₄','۴','٤',
                '４','⁵','₅','۵','٥','５','⁶','₆','۶','٦','６','⁷','₇','۷','７','⁸','₈','۸','８',
                '⁹','₉','۹','９','à','á','ả','ã','ạ','ă','ắ','ằ','ẳ','ẵ','ặ','â','ấ','ầ','ẩ','ẫ',
                'ᾆ','ᾇ','ὰ','ά','ᾰ','ᾱ','ᾲ','ᾳ','ᾴ','ᾶ','ᾷ','а','ﺃ','အ','ာ','ါ','ǻ','ǎ','ª','ა','अ
                ','ﺍ','ａ','ä','б','β','ﺏ','ဗ','ბ','ｂ','ç','ć','č','ĉ','ċ','ｃ','ď','ð','đ','ƌ',
                'ȡ','ɖ','ɗ','ᵭ','ᶁ','ᶑ','д','δ','ﺩ','ﺽ','ဍ','ဒ','დ','ｄ','é','è','ẻ','ẽ','ẹ','ê',
                'ľ','ĺ','ļ','ŀ','л','λ','ﻝ','လ','ლ','ｌ','м','μ','ﻡ','မ','მ','ｍ','ñ','ń','ň',
                'ộ','ơ','ớ','ờ','ở','ỡ','ợ','ø','ō','ő','ŏ','ο','ὀ','ὁ','ὂ','ὃ','ὄ','ὅ','ὸ',
                'ũ','ụ','ư','ứ','ừ','ử','ữ','ự','û','ū','ů','ű','ŭ','ų','µ','у','ဉ','ု','ူ','ǔ',
                'Ĩ','Ị','Î','Ï','Ī','Ĭ','Į','İ','Ι','Ί','Ϊ','Ἰ','Ἱ','Ἳ','Ἴ','Ἵ','Ἶ','Ἷ','Ῐ','Ῑ',
                'Ὶ','Ί','И','І','Ї','Ǐ','ϒ','Ｉ','Ｊ','К','Κ','Ｋ','Ĺ','Ł','Л','Λ','Ļ','Ľ','Ŀ',
		'Ὃ','Ὄ','Ὅ','Ὸ','Ό','О','Θ','Ө','Ǒ','Ǿ','Ｏ','Ö','П','Π','Ｐ','Ｑ','Ř','Ŕ','Р',
                'Ÿ','Ῠ','Ῡ','Ὺ','Ύ','Ы','Й','Υ','Ϋ','Ŷ','Ｙ','Ź','Ž','Ż','З','Ζ','Ｚ','Æ','Ǽ',
                'Ч','Ђ','Џ','Ĝ','Ĥ','IJ','Ĵ','Х','Љ','Њ','Œ','Ψ','Ш','Щ','ẞ','Þ','Ц','Я','Ю',
                'Ж',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ','　','ﾠ'];

echo "Hello World\n";
?>


Expected result:
----------------
When the opcache is loaded from a file the checksum in the file matches the computed checksum. No warning about a corrupted file in the logs.

Actual result:
--------------
In the opcache log the following warning shows up if the opcache bin file exists.

Warning corrupted file '/tmp/285d13c8bcb81a2cb747f9609f2e9b08/opt/php-src/ext/opcache/tests/adler32_checksum.php.bin'