Complain when a satpoint's offset is off the end of the output.

[gmart7t2]

When giving wallet send or wallet inscribe a satpoint with an invalid offset, ord crashes.

This fixes that.

Before:

$ ord wallet send --fee-rate 1 $addr $txid:0:9999999
thread 'main' panicked at 'Amount subtraction error', ~/.cargo/registry/src/github.com-1ecc6299db9ec823/bitcoin-0.29.2/src/util/amount.rs:722:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

After:

$ ord wallet send --fee-rate 1 $addr $txid:0:9999999
error: outgoing satpoint $txid:0:9999999 offset higher than maximum 1999