37c75c5820 test: wallet, fix change position out of range error (furszy)
Pull request description:
Fixes #29061. Only the benchmark is affected.
Since #25273, the behavior of 'inserting change at a random position'
is instructed by passing ´std::nullopt´ instead of -1.
Also, added missing documentation about the meaning of
'change_pos=std::nullopt' inside 'CWallet::CreateTransaction()'
ACKs for top commit:
achow101:
ACK 37c75c5820
kevkevinpal:
ACK [37c75c5](37c75c5820)
BrandonOdiwuor:
ACK 37c75c5820
Tree-SHA512: d9a8d8533540455716a5090fcf407573cad9f0d0018a05f903f89e51620302f9b256318db6f7338b85c047f7fab372d724e916b1721d7ed302dbf3d845b08734