oidmap: ensure map is initialized

Ensure that an oidmap is initialized before attempting to add, remove,
or retrieve an entry by simply performing the initialization step
before accessing the underlying hashmap.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

oidmap.c

@@ -33,12 +33,19 @@ void oidmap_free(struct oidmap *map, int free_entries)
 
 void *oidmap_get(const struct oidmap *map, const struct object_id *key)
 {
+	if (!map->map.cmpfn)
+		return NULL;
+
 	return hashmap_get_from_hash(&map->map, hash(key), key);
 }
 
 void *oidmap_remove(struct oidmap *map, const struct object_id *key)
 {
 	struct hashmap_entry entry;
+
+	if (!map->map.cmpfn)
+		oidmap_init(map, 0);
+
 	hashmap_entry_init(&entry, hash(key));
 	return hashmap_remove(&map->map, &entry, key);
 }
@@ -46,6 +53,10 @@ void *oidmap_remove(struct oidmap *map, const struct object_id *key)
 void *oidmap_put(struct oidmap *map, void *entry)
 {
 	struct oidmap_entry *to_put = entry;
+
+	if (!map->map.cmpfn)
+		oidmap_init(map, 0);
+
 	hashmap_entry_init(&to_put->internal_entry, hash(&to_put->oid));
 	return hashmap_put(&map->map, to_put);
 }