replace memset with string-list initializers

Using memset and then manually setting values of the string-list
members is not future proof as the internal representation of
string-list may change any time.
Use `string_list_init()` or STRING_LIST_INIT_* macros instead of
memset.

Signed-off-by: Tanay Abhra <tanayabh@gmail.com>
Reviewed-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/merge-recursive.c b/merge-recursive.c
index b5c3c53..4b648d9 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -2062,12 +2062,9 @@
 	if (o->verbosity >= 5)
 		o->buffer_output = 0;
 	strbuf_init(&o->obuf, 0);
-	memset(&o->current_file_set, 0, sizeof(struct string_list));
-	o->current_file_set.strdup_strings = 1;
-	memset(&o->current_directory_set, 0, sizeof(struct string_list));
-	o->current_directory_set.strdup_strings = 1;
-	memset(&o->df_conflict_file_set, 0, sizeof(struct string_list));
-	o->df_conflict_file_set.strdup_strings = 1;
+	string_list_init(&o->current_file_set, 1);
+	string_list_init(&o->current_directory_set, 1);
+	string_list_init(&o->df_conflict_file_set, 1);
 }
 
 int parse_merge_opt(struct merge_options *o, const char *s)