Region::interact fails in one configuration

With these regions (RBA::Region):

```
r1 = (0,10;0,290;280,290;280,230;360,230;360,70;280,70;280,10)
```

and

```
r2 = (360,70;360,230;480,230;480,70)
```

the interaction test renders an empty region:

```
r1.interacting(r2)
r2.interacting(r1)
```

However, these regions definitely touch.