Simulation broke by implementing a purpose

[CarstenBaumannH]

Hi,

overall the simulation is still a little bit unstable to test it intensively. Mostly I get an error "simulation broke" during creating a city before I can let the simulation run to grow the city.

The simulation broke error I got was the following:

WHAT HAPPENED:
called `Option::unwrap()` on a `None` value

WHERE IT HAPPENED:
at libcore\option.rs, line 345

WHERE EXACTLY:
stack backtrace:
   0:     0x7ff663609307 - <no info>
   1:     0x7ff663608b4e - <no info>
   2:     0x7ff663608bcd - <no info>
   3:     0x7ff6633b53ef - <no info>
   4:     0x7ff6636146f2 - <no info>
   5:     0x7ff663614254 - <no info>
   6:     0x7ff663614139 - <no info>
   7:     0x7ff6636345cc - <no info>
   8:     0x7ff6636344fe - <no info>
   9:     0x7ff6633dd619 - <no info>
  10:     0x7ff6633dc360 - <no info>
  11:     0x7ff663538c70 - <no info>
  12:     0x7ff6634377b9 - <no info>
  13:     0x7ff66358b1ce - <no info>
  14:     0x7ff66357d1c8 - <no info>
  15:     0x7ff663632fc2 - <no info>
  16:     0x7ff66358b446 - <no info>
  17:     0x7ff663277181 - <no info>
  18:     0x7ff663278dea - <no info>
  19:     0x7ff663632fc2 - <no info>
  20:     0x7ff663292cf5 - <no info>
  21:     0x7ff6636134e2 - <no info>
  22:     0x7ff663621a99 - <no info>
  23:     0x7ffc94523034 - BaseThreadInitThunk

It is always the line 345. Sometimes it happens while implementing a street to an already complex network of streets, sometimes by implementing a zone in a complex network of streets. See the picture below.