fix: crashing when viewing armor item with undefined resitances

[LordZanos]

Purpose of change

fix #4302

Items that are categorized as armor but don't have defined resistances will crash the game upon view.

Describe the solution

This was previously crash safe because we were using a null check, but the behavior was wrong. Added the null check back.

Describe alternatives you've considered

letting chaos scream and cry

Testing

Loaded up game, scrolled through entire debug spawner for items, no crash. Item resistance values look fine.

Additional context

Not a fix for INT_MIN physical resistance on some smaller items; I can't reproduce that issue on windows.

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