Added check if the last admin user is to be deleted, and if that's the case, prevent it and return with error message.

server/core/users.c

@@ -113,6 +113,10 @@ users_delete(USERS *users, char *user)
 int	del;
 
 	atomic_add(&users->stats.n_deletes, 1);
+        if (users->stats.n_entries == 1) {
+            atomic_add(&users->stats.n_entries, del * -1);
+            return 0;
+        }
 	del = hashtable_delete(users->data, user);
 	atomic_add(&users->stats.n_entries, del * -1);
 	return del;