Merge pull request libgit2#4027 from pks-t/pks/pack-deref-cache-on-error

pack: dereference cached pack entry on error

Author: carlosmn

src/pack.c

@@ -759,8 +759,11 @@ int git_packfile_unpack(
 	}
 
 cleanup:
-	if (error < 0)
+	if (error < 0) {
 		git__free(obj->data);
+		if (cached)
+			git_atomic_dec(&cached->refcount);
+	}
 
 	if (elem)
 		*obj_offset = curpos;