Traktor S4MK3: fix wheel mode not getting set correctly on deck switch - #16083

I am not sure to understand the bug and thus the fix. Could you provide actual reproduction steps and expected behaviour?

For reference, wheelMode and moveMode are expected to be undefined by default

1. set the preference to "alternative mode"
2. twist move knob on deck c -- it adjusts the move size
3. select deck d
4. select deck c
5. twist move knob on deck c -- it does a beatjump, because the movemode is wrong

you can also see the bug by inspection: we set the movemode to null, then we try to save the current move mode under currentModes -- that persists the null setting, not the original movemode setting as intended. also compare to 2.5, where saving currentMode happens before the nullifying.

that first block I noted can probably be removed, except that in the deck switch logic there is no "else" case for when seconddeck.modes is null -- what is meant to happen in that condition?

This PR is marked as stale because it has been open 90 days with no activity.

alternative mode is not in main, so this is actually blocked on #15664