shortlog: initialize mailmap

With this done, we can drop the extra initialization from
read_mailmap().

Author: peff

builtin/shortlog.c

@@ -373,6 +373,7 @@ void shortlog_init(struct shortlog *log)
 {
 	memset(log, 0, sizeof(*log));
 
+	mailmap_init(&log->mailmap);
 	read_mailmap(the_repository, &log->mailmap);
 
 	log->entries = kh_init_shortlog();

mailmap.c

@@ -221,7 +221,6 @@ int read_mailmap(struct repository *repo, struct mailmap *map)
 	repo_config_get_pathname(repo, "mailmap.file", &mailmap_file);
 	repo_config_get_string(repo, "mailmap.blob", &mailmap_blob);
 
-	string_list_init_dup(&map->map);
 	map->map.cmp = namemap_cmp;
 
 	if (!mailmap_blob && is_bare_repository())