Bug#12543706 - innodb-fast-shutdown=2: Assert

node->modification_counter == node->flush_counter

This bug (an assertion failure during a crash-like shutdown)
was introduced by the fix of
Bug#12323643 Clean up the InnoDB thread shutdown and assertions (WL#5136).

fil_node_close_file(): Relax the failing assertion
when innodb_fast_shutdown=2.

storage/innobase/fil/fil0fil.c

@@ -856,7 +856,8 @@ fil_node_close_file(
 	ut_a(node->open);
 	ut_a(node->n_pending == 0);
 	ut_a(node->n_pending_flushes == 0);
-	ut_a(node->modification_counter == node->flush_counter);
+	ut_a(node->modification_counter == node->flush_counter
+	     || srv_fast_shutdown == 2);
 
 	ret = os_file_close(node->handle);
 	ut_a(ret);