When producing a dummy signature for the purpose of estimating the transaction fee, do not assume an external signer performs R-value grinding on the signature.
In particular, this avoids a scenario where the fee rate is 1 sat / vbyte and a transaction with a 72 byte signature is not accepted into our mempool.
This commit also drops the nullptr default for CCoinControl arguments for functions that it touches. This is because having a boolean argument right next to an optional pointer is error prone.
Co-Authored-By: S3RK <1466284+S3RK@users.noreply.github.com>