Special Z characters are either erased or mis-substituted

[Namely]

Function convert_chars defined in wp-includes/formatting.php and used in many filters in wp-includes/default-filters.php does not handle two characters properly.

The subjects are two special Z characters: "Ž" and "ž".

convert_chars performs the following replacements:

	$wp_htmltranswinuni = array(
...
	'Ž' => 'ž',
...
	'ž' => '',
...

This lower-cases "Ž" to "ž" and also erases "ž".

Instead, the code should be as follows:

	$wp_htmltranswinuni = array(
...
	'Ž' => 'Ž',
...
	'ž' => 'ž',
...

[SergeyBiryukov]

That's a valid change indeed.

0x8E	0x017D	#LATIN CAPITAL LETTER Z WITH CARON
0x9E	0x017E	#LATIN SMALL LETTER Z WITH CARON

​http://unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WINDOWS/CP1252.TXT

Unit test: ​[UT694]

[nacin]

In [20653]:

Properly convert two special Z characters in convert_chars(). props Namely, SergeyBiryukov. fixes #20503.