libast: utf8_mbtowc(): Fix utf8tab to match new type (re: ccc707c)

Given this:

	if ((m = utf8tab[*sp]) > 0)

it was not correct to change the type of m to size_t because that's
an unsigned type, while utf8tab[] contains two final entries of -1.

However, since utf8_mbtowc otherwise treats -1 exactly the same way
as 0, and nothing else uses that table, it's enough just to change
those values to 0.

Author: McDutchie

src/lib/libast/comp/setlocale.c

@@ -484,7 +484,7 @@ static const uint32_t		utf8mask[] =
 	0xfc000000,
 };
 
-static const signed char	utf8tab[256] =
+static const unsigned char	utf8tab[256] =
 {
 	0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
 	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
@@ -501,7 +501,7 @@ static const signed char	utf8tab[256] =
 	2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
 	2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
 	3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
-	4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6,-1,-1,
+	4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 0, 0,
 };
 
 static int