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>

Co-Authored-By: bob-the-kuhn <bob.kuhn@att.net>

Reference #13156

Reference #13250

Addressing #13231

Ticket #13228

If `INCH_MODE_SUPPORT` is undefined, G20 is an unknown command as it should be (Marlin is, by default, operating in metric mode). G21, however, is found in many slicers and printer start gcode sections and should be accepted (as a NOOP) to avoid the unknown commands.

Fix #12643
Only factors above 1 can have a 'positive' effect.