fix: correct exchange rate calculation for taken range orders

[keshav0479]

Fixes #2336

Problem

For range orders, the "You receive" satoshi amount in the Order tab showed an incorrect (lower) value after the order was taken.

Cause

The rate calculation used max_amount whenever has_range was true, even after the order was taken and amount was set to the actual taken value. This caused a math mismatch:

• satoshis_now was computed for the taken amount (eg 800 EUR)
• rate was computed incorrectly using max_amount (eg 1000 EUR)

Fix

Changed the rate calculation to prioritize order.amount (the actual taken amount) when available. It falls back to max_amount only for untaken range orders.

[KoalaSat]

@keshav0479 Thanks for taking care of this!

Please accept a small tip for your work. Share here a LN invoice with long expiration date for 35,000 sats

[keshav0479]

Thank you @KoalaSat! I really appreciate the review and the tip.

lnbc350u1p54e7happ5pxjgfjehf2uw3kj0p8x3cudyk3pyf9w69tsdyd2stfesx8h6p2xqcqzyssp5djelhlapyhgdre040ulwq7raml9efm5xauv9l6n8s9hp6nxjpqrq9q7sqqqqqqqqqqqqqqqqqqqsqqqqqysgqdqqmqz9gxqyjw5qrzjqwryaup9lh50kkranzgcdnn2fgvx390wgj5jd07rwr3vxeje0glcll63a0scqz7stsqqqqlgqqqqqeqqjqxvjgjpcq6hrwwj9ugyjpavukl7sun0pfut4ghzcwku60264ldepx2tss8v4a4yv7jnfnpn87v2y8m9wesdtj6kngcrgqkepzakcfc8cq49008x

[RobosatsDevFund]

@keshav0479 Seems like it is not possible to pay this invoice due to either your channels are full and your node is and Robosats' node is poorly connected. You can try with a proxy wallet.

[keshav0479]

@keshav0479 Seems like it is not possible to pay this invoice due to either your channels are full and your node is and Robosats' node is poorly connected. You can try with a proxy wallet.

lnbc350u1p54lqtkpp5p8lgw566cpujcf2umd002jvyw3psetrms53fmj3fss79a9h2xy5sdqqcqzzsxqyz5vqsp5qvda07ev5qavmrlj2we5w75p7etfaw3l08vp6axp452pu6j3227q9qxpqysgqcx8l6sd6kwlvn7d2v9pjtsgma5gfvgctr0847aqgjdg4xeyglx95wvj5jetzz5palzg6gmtht9nj8g8av9nxdqxjdlk74srxppe0m4speefc5n

[RobosatsDevFund]

7390939451b5ae8f9942040ba440325e463d1656553f327f530908e81be098ab