readdir() returns inaccessible name if file was created with invalid UTF-8

[Andrew Schulman]

>> Testcase (attached):
>
>Thanks for the testcase!
>
>I found the problem in the newlib core function creating wchar_t from
>UTF-8 input.  In case of 4 byte UTF-8 sequences, the code created the
>low surrogate already after reading byte 3, without checking if byte 4
>of the UTF-8 sequence is a valid byte. Hilarity ensues.
>
>Fortunately this bug has only been introduced very recently, to wit, on
>2009-03-24, a mere 16 years ago.  And it is my bug and mine alone :}
>
>I'm just prep'ing a fix which I'll push in a minute or two.

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