assert in listing 5.5 never fire

[icyhearts]

Thanks for your book and code.
I tested code in listing 5.5.
The book says, in the code in Listing 5.5 the assert can fire, but I tested it and the assert never fire:

mi.U18|icefire|2021-12-29 13:06:30[muice@ listings]g++ listing_5.5.cpp -pthread
mi.U18|icefire|2021-12-29 13:07:18[muice@ listings]./a.out 
mi.U18|icefire|2021-12-29 13:07:20[muice@ listings]echo $?
0
mi.U18|icefire|2021-12-29 13:07:24[muice@ listings]./a.out 
mi.U18|icefire|2021-12-29 13:09:27[muice@ listings]echo $?
0

Test environement:
CPU: Intel(R) Core(TM) i7-9700 CPU @ 3.00GHz
g++ version: g++ (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
os version: Ubuntu 18.04.4