Fix wait_for_empty calls in concurrent testing
diff --git a/test/tester.es b/test/tester.es
index e6a4701..e0a28e5 100755
--- a/test/tester.es
+++ b/test/tester.es
@@ -656,7 +656,7 @@
 
 execute(_TxObj, St, <<"WAIT_EMPTY">>) ->
     Prefix = stack_pop(St),
-    wait_for_empty(St, Prefix),
+    wait_for_empty(St#st.db, Prefix),
     stack_push(St, <<"WAITED_FOR_EMPTY">>),
     St;