Fix edge cases for run sequence generation

[Peque]

We currently take a step front until we are not in a goal cell. This is safe normally because the goal area has no walls in it. However, what happens if the goal area is next to the maze outline? Will we step out of the maze? Specially in half-size mazes, where those position jumps are not "protected" by the fact that the maze area matches the uint_t type holding it.

We should probably add a test for this.

097a447117829fa1458fd9022debae74bc6c473b