"MIDI for light" mapping tries to kill a non-existent timer

[fwcd]

Bug Description

I've had some issues running this mapping lately. I've been getting errors of the form

Uncaught exception: file:///Applications/Mixxx.app/Contents/Resources/controllers/Midi_for_light-scripts.js:105: TypeError: Cannot read property '0' of undefined
Backtrace: @file:///Applications/Mixxx.app/Contents/Resources/controllers/Midi_for_light-scripts.js:105

and a bunch of log messages

warning [Controller] "Tried to kill Timer \"0\" that does not exists"
warning [Controller] "Tried to kill Timer \"0\" that does not exists"
warning [Controller] "Tried to kill Timer \"0\" that does not exists"
warning [Controller] "Tried to kill Timer \"0\" that does not exists"

The MIDI device I am trying to run it with is a virtual loopback port (midilink). Not sure what went wrong here, since I have already been successfully running this configuration on another machine, will have to dig into this...

Version

2.5-alpha-329-g59a4374a44 (HEAD)

(though this also seems to happen in 2.4 builds)

OS

macOS 14.3.1

[fwcd]

I have noticed that the MIDI for light mapping only seems to work in isolation, but not if another physical controller (e.g. the MC7000) has an enabled mapping. The MC7000 works fine, but the "MIDI for light" MIDI port doesn't receive any beat/BPM messages on the other end... VU messages seem to work fine in all cases though.

Edit: The issue seems to have been that the active track is only detected based on the crossfader position (even if both decks are "through") and not based on the faders (like e.g. the active deck shown in the window's title bar)