From PHP 7.4,fwrite function now returns false for any failure:https://www.php.net/manual/en/migration74.incompatible.php#migration74.incompatible.core.fread-fwrite

Actually, the note in the PHP documentation is not exact: for PHP 7.3 and lower,fwrite function did return false when arguments passed in to the function were invalid, and 0 for other failures. From PHP 7.4, it returns false for any failure.
We can see it in the source code: for PHP 7.3:https://github.com/php/php-src/blob/a1a8d144854acb1c891cf0c21abb0f612b1d8de7/ext/standard/file.c#L1140
Compare to PHP 7.4:https://github.com/php/php-src/blob/master/ext/standard/file.c#L1136

I updateOutputStream::doWrite() to keep the same behavior as before.