Don't try to insert maps if there are none

src/db_query.c

@@ -414,6 +414,10 @@ int64_t syncIdMap(struct stored_conn_t *sconn, const char *table, size_t table_l
     return qry_ret;
   }
 
+  if (n_maps == 0) {
+    return 1;
+  }
+
   if ((sb = strbld_create()) == 0) {
     return -1;
   }