[Bug]: Monero (XMR) invoice shows wrong destination of additional payment

[NicolasDorier]

Reposting for @d2ro

btcpayserver/btcpayserver#7204

[napoly]

Please note: the partial payment flow has an issue.. it should not be possible to fully repay an invoice by paying 50% twice.. each partial payment should include a network fee, so two 50% payments would leave a small remainder requiring a third payment to fully settle.. fyi

Root cause seems to be the fee underestimation from #1 ..the fee is so small it's effectively invisible..