git-apply --whitespace=fix: fix off by one thinko

When a patch adds a whitespace followed by end-of-line, the
trailing whitespace error was detected correctly but was not
fixed, due to misconversion in 42ab241 (builtin-apply.c: do not
feed copy_wsfix() leading '+').

Signed-off-by: Junio C Hamano <gitster@pobox.com>

ws.c

@@ -234,7 +234,7 @@ int ws_fix_copy(char *dst, const char *src, int len, unsigned ws_rule, int *erro
 	 * Strip trailing whitespace
 	 */
 	if ((ws_rule & WS_TRAILING_SPACE) &&
-	    (2 < len && isspace(src[len-2]))) {
+	    (2 <= len && isspace(src[len-2]))) {
 		if (src[len - 1] == '\n') {
 			add_nl_to_tail = 1;
 			len--;