Update CScriptNetPropManager

[samisalreadytaken]

The warning message is quite important, it's easy to make typos and not be aware of it ever.

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PR Checklist

• My PR follows all guidelines in the CONTRIBUTING.md file
• My PR targets a develop branch OR targets another branch with a specific goal in mind

[azzyr]

looks good to me otherwise, i'll close #535

[azzyr]

is there a particular reason for removing these lower bound checks? index is provided by the user so this seems scary

[samisalreadytaken]

Unsigned cast of all negative numbers ([-1, -2147483648] -> [2147483648, 4294967295]) is always larger than the limit. It compiles into same code with less instructions (0-test) because arraysize is always non-zero.

If, on 64-bit, this function were to take a 64-bit signed index and this unsigned cast stayed 32-bit, values in the range [0x8000000000000000, 0x800000007fffffff] would truncate the sign bit and access out of bounds, but that's a lot of unlikely ifs.

I added some more assertions and a comment to inform future editors. This isn't a super important change though, impact of these 2 instructions is negligible