Bug: Blog image breaks formatting when it ends at a certain place

Problem identified: The text here:

the “10% in Vermont” local investment program.

has multibyte characters for the fancy quotation marks, and that throws off substr_replace which is not multibyte safe.

Surprisingly little discussion about dealing with this. There's https://github.com/wpsharks/comet-cache/issues/703 and,

from https://sourceforge.net/p/wikindx/svn/HEAD/tree/trunk/core/libs/UTF8.php comes one replacement function:

    /**
     * Simulate substr_replace() for multibytes strings
     *
     * @param string $string
     * @param string $replacement
     * @param int $start
     * @param int $length Default is NULL.
     * @param string $encoding Default is NULL.
     *
     * @return string
     */
    function mb_substr_replace($string, $replacement, $start, $length = NULL, $encoding = NULL)
    {
        $string_length = (is_null($encoding) === TRUE) ? mb_strlen($string) : mb_strlen($string, $encoding);

        if ($start < 0)
        {
            $start = max(0, $string_length + $start);
        }
        elseif ($start > $string_length)
        {
            $start = $string_length;
        }

        if ($length < 0)
        {
            $length = max(0, $string_length - $start + $length);
        }
        elseif ((is_null($length) === TRUE) || ($length > $string_length))
        {
            $length = $string_length;
        }

        if (($start + $length) > $string_length)
        {
            $length = $string_length - $start;
        }

        if (is_null($encoding) === TRUE)
        {
            return mb_substr($string, 0, $start) . $replacement . mb_substr($string, $start + $length, $string_length - $start - $length);
        }

        return mb_substr($string, 0, $start, $encoding) . $replacement . mb_substr($string, $start + $length, $string_length - $start - $length, $encoding);
    }

But it turns out we could use an even more simple version of a simple version suggested in the PHP manual for substr_replace here https://www.php.net/manual/en/function.substr-replace.php#48066