Potential fix for code scanning alert no. 41: Size computation for allocation may overflow

[fabriziosalmi]

Potential fix for https://github.com/fabriziosalmi/caddy-waf/security/code-scanning/41

To fix the problem, we need to ensure that the arithmetic operation involving the lengths of the slices does not overflow. This can be achieved by validating the lengths of the slices before performing the arithmetic operation. Specifically, we should check if the sum of the lengths of customFields and commonFields exceeds the maximum value for the type before using it in the allocation.

1. Add a check to validate the lengths of customFields and commonFields before performing the arithmetic operation.
2. If the combined length exceeds the maximum value for the type, handle the error appropriately (e.g., by logging an error message and returning an error).

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