Impassable wall in oasis map

Bug Report ID: #4274084509

Bug is simple. The mapgen made it so there was an impenetrable wall in the map, blocking off the last rare.

Luckily it didn't block my map progression (I could Storm Lance past/into the wall) and the loot I didn't get wasn't too important (a rare solar amulet and a waystone) but this shouldn't happen in map generaiton.