* string/strxfrm_l.c (STRXFRM): Fix trailing \1 optimization

if N is one bigger than return value.
	* string/tst-strxfrm2.c (do_test): Also test strxfrm with l1 + 1
	and l1 last arguments, if buf is defined, verify the return value
	equals to strlen (buf) and verify no byte beyond passed length
	is modified.

string/strxfrm_l.c

@@ -432,7 +432,7 @@ STRXFRM (STRING_TYPE *dest, const STRING_TYPE *src, size_t n, __locale_t l)
   if (needed > 2 && needed == last_needed + 1)
     {
       /* Remove the \1 byte.  */
-      if (--needed < n)
+      if (--needed <= n)
 	dest[needed - 1] = L('\0');
     }