conversion: don't crash when no destination algo

When we set up a repository that doesn't have a compatibility hash
algorithm, we set the destination algorithm object to NULL.  In such a
case, we want to silently do nothing instead of crashing, so simply
treat the operation as a no-op and copy the object ID.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: bk2204

object-file-convert.c

@@ -23,7 +23,7 @@ int repo_oid_to_algop(struct repository *repo, const struct object_id *src,
 	const struct git_hash_algo *from =
 		src->algo ? &hash_algos[src->algo] : repo->hash_algo;
 
-	if (from == to) {
+	if (from == to || !to) {
 		if (src != dest)
 			oidcpy(dest, src);
 		return 0;