See #12731

See #12981

See #13267

When `count()` returns 0, `pos > (count()-1)` will always yield `true` due to integer underflow.

To eliminate a long delay during pause, park, and filament change

- The `sdcard.transfer_port` variable is Marlin's internal serial port index, not the physical serial port number.
- Added packet number to "ok" response so hosts don't need to wait for the ACK.
- Renamed feature to `BINARY_FILE_TRANSFER`, as the speed up is only consequential to the ability to transfer binaries over serial.

Counterpart to #12845

Co-Authored-By: Msq001 <msq001@users.noreply.github.com>