DungeonJob.PostGenWallMount: better error handling

[whatston3]

About the PR

Added error checks to dungen wallmount jobs to avoid throwing exceptions.

Why / Balance

Dungeon generation was failing, and this caused expedition computers to get stuck.

As a note, the Mineshaft expeditions seem terrible, they're open corridors in something that may not be entirely rock.

How to test

1. Buy an expedition ship.
2. Go on an expedition to a Caves biome (more likely to have Haunted, Mineshaft expedition types).
3. The expedition should go through, you should warp as normal and not get stuck.
4. Repeat steps 2-4 until satisfied.

Media

• I have added screenshots/videos to this PR showcasing its changes ingame, or this PR does not require an ingame showcase

Breaking changes

Changelog

🆑

• fix: An issue causing salvage expedition consoles to get stuck has been resolved.

[dvir001]

DIdnt test in game yet but the code change looks sane.

[whatston3]

Somewhat related - while we're editing dungeon generation stuff, we could add WallRock walls to the mineshaft definition variants so they aren't just out and open. Should make the thing more believable/less scuffed at the very least.