[BUG] - Panic at parsing specific 11 digit strings

[igorkova]

Context

personnummer.Valid("19000011111")

Expected outcome

false

Actual outcome

panic

Description

Looks like all 11 digit inputs are panicking.

I am not sure about all the details regarding the length of PN, coordination number and interim numbers but it feels like we could do a check on the length and make sure that we are dealing with 10 or 12 digits at all times?
I see we have length check already for == 0 and < 8 https://github.com/personnummer/go/blob/master/personnummer.go#L214 which discourages me to put 10/12 check as it's unclear why 9 would be OK.

Minimal reproducible test case

[frozzare]

Thanks, you're right. I've fixed this before you're pull request since I've could remove some code and move around some code to make it work without the if.