[reservoir] make missing payment data a panic
[reservoir] make missing payment data a panic

This will only occur if the reservoir data is corrupt
Make panic rather than continuing wil faulty data

Signed-off-by: Christopher Hall <97c3bc3fef1a71b149f1095f758464e4b18eb35b@bitmark.com>

bitmark-inc/bitmarkd,bitmark-inc/bitmarkd