[BUG] getActiveTrack crashes when chaining patterns if the next patter does not have the active track

[ajboni]

When a pattern chains to another, and the next patter does not includes the current active track, it crashes the application

Reproduce:

1. set up pattern chaining p1 to p2
2. add a track to p1, focus on this new track
3. press play
4. wait the chain to apply. Notice crash.

Caught panic:

runtime error: index out of range [3] with length 1

Restoring terminal...

goroutine 1 [running]:
runtime/debug.Stack()
        /usr/lib/go/src/runtime/debug/stack.go:24 +0x5e
runtime/debug.PrintStack()
        /usr/lib/go/src/runtime/debug/stack.go:16 +0x13
github.com/charmbracelet/bubbletea.(*Program).Run.func1()
        /home/baj/go/pkg/mod/github.com/charmbracelet/[email protected]/tea.go:479 +0x91
panic({0x593b60?, 0xc0003142b8?})
        /usr/lib/go/src/runtime/panic.go:770 +0x132
sektron/ui.(*mainModel).getActiveTrack(...)
        /home/baj/git/sektron/ui/ui.go:406
sektron/ui.mainModel.renderTransport({{0x5ff8b8, 0xc0000c85a0}, {{0xc000256008, 0x8a, 0xff}, {0xc000260008, 0x89, 0xbf}, 0xc000190030, {0x0, ...}, ...}, ...})
        /home/baj/git/sektron/ui/transport.go:68 +0x510
sektron/ui.mainModel.View({{0x5ff8b8, 0xc0000c85a0}, {{0xc000256008, 0x8a, 0xff}, {0xc000260008, 0x89, 0xbf}, 0xc000190030, {0x0, ...}, ...}, ...})
        /home/baj/git/sektron/ui/ui.go:384 +0x3d
github.com/charmbracelet/bubbletea.(*Program).eventLoop(0xc000234100, {0x5fe4e8?, 0xc000320008?}, 0xc0000256e0)
        /home/baj/go/pkg/mod/github.com/charmbracelet/[email protected]/tea.go:414 +0x707
github.com/charmbracelet/bubbletea.(*Program).Run(0xc000234100)
        /home/baj/go/pkg/mod/github.com/charmbracelet/[email protected]/tea.go:550 +0xa0e
main.main()
        /home/baj/git/sektron/main.go:45 +0x478