strange behavior while building roads that cross themselves

[MiniDigger]

this is the road I was trying to build (in three steps)

sometimes it crashes like this:

sometimes it doesn't build the circle:

the roads are still there, they just don't get build:

when you click the "ghost roads", you get this exception:

thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', ../src/libcore\option.rs:323
note: Run with `RUST_BACKTRACE=1` for a backtrace.
Simulation Panic!
"called `Option::unwrap()` on a `None` value"
thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', ../src/libcore\option.rs:323```

[Tomnewsom]

Duplicate of #35

[aeplay]

Closing as duplicate of #35