split: invalid number of chunks: '18446744073709551616'

[oech3]

At tag/laest-commit:

$ split --number=18446744073709551616
split: invalid number of chunks: '18446744073709551616'

[naoNao89]

hmm, GNU accepts e <= OVERFLOW_OK, meaning overflow is allowed while still validating n > 0. just accept input, clamp to u64::MAX for matching GNU behavior