Raised Metal Corners are indestructible

## Testmerges
#9427: 'external authentication system' by hry-gh at commit ed1c34e66f
#9493: 'The Overthrall & Blooded Thralls' by MeH0y at commit 2cb1fc47de
#8878: 'Whiskey Outpost Xenofication' by Unknownity at commit d90e311487
#8570: 'Sexier Sprites & The Soulening of Spitting' by BasilHerb at commit 759e657aa6
#9193: 'Trijent Z levels' by BOBAMAx at commit 0639df1543
#9590: 'Multi Z Almayer [MDB IGNORE]' by spartanbobby at commit f4dd5251a9

## Round ID
28619

## Description of the bug
Raised Metal Corners, as opposed to raised metal ledges, are indestructible and cannot be destroyed by conventional methods. I have shot them with brute rockets and placed C4 nearby, but they do not get destroyed.

## What's the difference with what should have happened?
The raised metal corner should be destroyed upon explosives and allow for cades to be placed in that tile.

## How do we reproduce this bug?
Step 1. Have a raised metal corner.
Step 2. Attempt to destroy it by any means.
Step 3. (optional). Wail in terror.

## Attached logs
```
N/A
```

## Additional details
- Author: Jesters_Ballad
- Admin: SmellyHippie
- Note: None