This would have tried to send a second output to make the tx
look like the 2/2 ideal, but it would not fail to find one
because picking an output from preferred_inputs priority list
did not remove it from the unused tranfer/dust outputs, so
it would try to send the same output twice.
While there, I also added a check to avoid sending a second
input if it's related to the first. Better 1/2 than linking
inputs, I think.
moneromooo-monero
20f7152769