Router SendPayment does not parse Amount when Invoice with dynamic value is set.

Nobody has claimed this yet.

https://github.com/lightninglabs/lndclient/blob/67d851af8b541c231dd9bd1abb1842eba05a4dfe/router_client.go#L425

When sending a payment with the parameters request.Invoice set to a 0 amount invoice as well as request.Amount set it will still submit it without the amount as opposed to what is expected for a dynamic value invoice.

I tried it with [this](https://lndecode.com/?invoice=lnbcrt1pjmspe8pp5kq8kqv62c59cmaku5zwvruhnelm9824h0kwktukcswa8qq32767qdqjwfskuer0d5sxumm5v5cqzzsxqyz5vqsp50mn0lqkhuxk37mdatlsuc8e85s8dcs0ktwzm348k9edslj50evqq9qyyssq4jnwf003rzc7p4vpnq7vr668vf65lnzrepzc55m4lvrfmgzg3hdz9nx2qhsx4k9xjrms5e0mgnmfglehrlztv2ca9kzgevhjuw6wuacqwpr477) invoice. This will result in `rpc error: code = Unknown desc = amount must be specified when paying a zero amount invoice`

Or is this expected and I have to replace the 0 amount invoice myself first?

Start at router_client.go around line 425 and reproduce the request using a zero-amount invoice with request.Amount set. Confirm how SendPayment handles the invoice and amount, then add coverage showing that the requested amount is passed for dynamic-value invoices and that the reported RPC error no longer occurs.

Written by the indexing model from the issue text.