[GAME] Map-specific custom weapons cause the game to crash after loading 2 other maps in succession

[Blixibon]

Describe the bug

Custom weapons defined on a map-specific basis using Petercov's custom weapons framework (i.e. custom weapons defined by manifests such as %mapname%_weapons.txt) cause the game to crash when loading another map, and then loading another map afterwards.

Steps to reproduce

Steps to reproduce the behavior:

1. Have a custom weapon defined in a level
2. Load a different map that does not have a custom weapon
3. Load any other map
4. See error

Expected behavior

Custom weapons should not crash the game.

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Additional context

I did not thoroughly test this issue because I am preparing for an unrelated release. All I did was isolate it to the custom weapon scripts provided by the initial pull request. It's possible this issue is narrower or broader than map-specific custom weapons.