fix iconv conversions for iso88592-iso885916

commit 97bd6b09dbe7478d5a90a06ecd9e5b59389d8eb9 refactored the table
lookup into a function and introduced an error in index computation.
the error caused garbage to be read from the table if the given charmap
had a non-zero number of elided entries.

src/locale/iconv.c

@@ -153,7 +153,7 @@ static void put_32(unsigned char *s, unsigned c, int e)
 
 static unsigned legacy_map(const unsigned char *map, unsigned c)
 {
-	unsigned x = c - 128 + map[-1];
+	unsigned x = c - 128 - map[-1];
 	x = legacy_chars[ map[x*5/4]>>2*x%8 |
 		map[x*5/4+1]<<8-2*x%8 & 1023 ];
 	return x ? x : c;