In decodepsbt if an invalid amount is seen, don't calculate the fee
but still show the invalid value in the decode.
In analyze psbt, if an invalid amount is seen, set the next step to
be the creator as the creator needs to remake the transaction so that
it is valid.
psbt.cpp definitions except for AnalyzePSBT are used by the wallet and need to
be linked into the wallet binary. AnalyzePSBT is an exception in that it is not
used by the wallet, and depends on node classes like CCoinsViewCache, and on
node global variables like nBytesPerSigOp.
So AnalyzePSBT is more at home in libbitcoin_server than libbitcoin_common, and
in any case needs to be defined in a separate object file than other PSBT
utilities, to avoid dragging link dependencies on node functions and global
variables into the wallet.
