Fix severe breakage in "git-apply --whitespace=fix"

735c674 (Trailing whitespace and no newline fix, 2009-07-22) completely
broke --whitespace=fix, causing it to lose all the empty lines in a patch.

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

Author: gitster

t/t4124-apply-ws-rule.sh

@@ -154,16 +154,20 @@ create_patch () {
 		index e69de29..8bd6648 100644
 		--- a/target
 		+++ b/target
-		@@ -0,0 +1 @@
+		@@ -0,0 +1,3 @@
+		+An empty line follows
+		+
 		+A line with trailing whitespace and no newline_
 		\ No newline at end of file
 	EOF
 }
 
 test_expect_success 'trailing whitespace & no newline at the end of file' '
 	>target &&
-	create_patch | git apply --whitespace=fix - &&
-	grep "newline$" target
+	create_patch >patch-file &&
+	git apply --whitespace=fix patch-file &&
+	grep "newline$" target &&
+	grep "^$" target
 '
 
 test_done

ws.c

@@ -262,10 +262,10 @@ 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) {
-		if (1 < len && src[len - 1] == '\n') {
+		if (0 < len && src[len - 1] == '\n') {
 			add_nl_to_tail = 1;
 			len--;
-			if (1 < len && src[len - 1] == '\r') {
+			if (0 < len && src[len - 1] == '\r') {
 				add_cr_to_tail = !!(ws_rule & WS_CR_AT_EOL);
 				len--;
 			}