Short Name field sanitization does not account for multi-byte characters

[westonruter]

As reported by @RavanH:

By the way, I just found that if I set a 12 character Short Name with special character in it, like “On the Rhône” it will get cut off at 11 characters after saving. The short name with a simple “o” instead of the “ô” does not suffer this issue.

Yes, this is due to having used substr() instead of mb_substr() in sanitize_short_name. I can see that using the latter will fix the issue: https://3v4l.org/DeJdr

Note that we are using the multibyte-safe function in is_name_short:

pwa-wp/wp-includes/class-wp-web-app-manifest.php

Lines 191 to 195 in 456f039

	public function is_name_short( $name ) {
	$name = trim( $name );
	$length = function_exists( 'mb_strlen' ) ? mb_strlen( $name ) : strlen( $name );
	return $length <= self::SHORT_NAME_MAX_LENGTH;
	}

We just need to use it in sanitize_short_name as well.