Don't crash when `fees` in undefined

[Empty2k12]

Max managed to get a transaction which was manually closed by Velo in the database and which has no fees field in the /bookings endpoint.

Not sure what the best fix is? Assume everything nullable and provide a default for every field?

[NeoLegends]

I guess we can special-case this occurency by maling the fee field 0, or we extend the logic to tread falsy values there as 0, basically turning kff „strict“ comparisons for that value.