revert: fix tiny memory leak in cherry-pick --ff

We forgot to free defmsg when returning early for a fast-forward.

Fixing this should reduce noise during test suite runs with valgrind.
More importantly, once cherry-pick learns to pick multiple commits,
the amount of memory leaked would start to add up.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-revert.c

diff --git a/builtin-revert.c b/builtin-revert.c
index 476f41e..9a3c14c 100644
--- a/builtin-revert.c
+++ b/builtin-revert.c
@@ -274,7 +274,7 @@
 	int i, index_fd, clean;
 	char *oneline, *reencoded_message = NULL;
 	const char *message, *encoding;
-	char *defmsg = git_pathdup("MERGE_MSG");
+	char *defmsg = NULL;
 	struct merge_options o;
 	struct tree *result, *next_tree, *base_tree, *head_tree;
 	static struct lock_file index_lock;
@@ -364,6 +364,7 @@
 	 * reverse of it if we are revert.
 	 */
 
+	defmsg = git_pathdup("MERGE_MSG");
 	msg_fd = hold_lock_file_for_update(&msg_file, defmsg,
 					   LOCK_DIE_ON_ERROR);