builtin/difftool.c: { 0 }-initialize rather than using memset()

Refactor an initialization of a variable added in
03831ef (difftool: implement the functionality in the builtin,
2017-01-19). This refactoring makes a subsequent change smaller.

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Acked-by: Derrick Stolee <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

builtin/difftool.c

@@ -361,7 +361,7 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 	struct hashmap symlinks2 = HASHMAP_INIT(pair_cmp, NULL);
 	struct hashmap_iter iter;
 	struct pair_entry *entry;
-	struct index_state wtindex;
+	struct index_state wtindex = { 0 };
 	struct checkout lstate, rstate;
 	int err = 0;
 	struct child_process cmd = CHILD_PROCESS_INIT;
@@ -387,8 +387,6 @@ static int run_dir_diff(const char *extcmd, int symlinks, const char *prefix,
 	mkdir(ldir.buf, 0700);
 	mkdir(rdir.buf, 0700);
 
-	memset(&wtindex, 0, sizeof(wtindex));
-
 	memset(&lstate, 0, sizeof(lstate));
 	lstate.base_dir = lbase_dir = xstrdup(ldir.buf);
 	lstate.base_dir_len = ldir.len;