[b31] escort portal gone after digging a wall

[Marbat]

During an escort mission in trollmire, I dug through a tree with some pickaxe. The portal was right behind it, and, somehow, the portal tile disappeared (plain vanilla grass). Still, the escort was running to the location the portal was supposed to be. When he reached it, the mission did not complete and the escort kept standing there, doing nothing.

[darkgod]

fixed