nls: utf8_wcstombs: use correct buffer size in error case

When utf8_wcstombs encounters a character that cannot be encoded, we
must not decrease the remaining output buffer size because nothing has
been written to the output buffer.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/nls/nls_base.c

@@ -144,7 +144,6 @@ utf8_wcstombs(__u8 *s, const wchar_t *pwcs, int maxlen)
 			size = utf8_wctomb(op, *ip, maxlen);
 			if (size == -1) {
 				/* Ignore character and move on */
-				maxlen--;
 			} else {
 				op += size;
 				maxlen -= size;