Fix assertion with --innodb-sync-debug=ON

srv_purge_wakeup() is called under protection of latch in
purge_sys_t::resume()

move sync check code before acquiring that latch.

storage/innobase/srv/srv0srv.cc

@@ -2290,8 +2290,6 @@ void
 srv_purge_wakeup()
 {
 	ut_ad(!srv_read_only_mode);
-	ut_ad(!sync_check_iterate(sync_check()));
-
 	if (srv_force_recovery >= SRV_FORCE_NO_BACKGROUND) {
 		return;
 	}

storage/innobase/trx/trx0purge.cc

@@ -1349,7 +1349,7 @@ void purge_sys_t::resume()
      ut_ad(!srv_undo_sources);
      return;
    }
-
+   ut_ad(!sync_check_iterate(sync_check()));
    rw_lock_x_lock(&latch);
    int32_t paused= m_paused--;
    ut_a(paused);