Fixes issue with trying to access tick.label when using Sankey chart

[FadhlurZ]

Fix: Add null checks for Sankey chart compatibility

Problem:
The plugin crashes when rendering Sankey charts with the following error:
TypeError: Cannot read properties of undefined (reading 'label')

Root Cause:
In the bindChartEvents function, the code assumes all chart axes have tickPositions and that axis.ticks[pos] will always return a valid tick object. However, Sankey charts don't use traditional axes with ticks, causing:

• axis.tickPositions to be undefined
• axis.ticks[pos] to return undefined for certain positions

Solution:
Added null/undefined checks before accessing tick properties:

// Before
if (axis.ticks) {
    const tickPositions = axis.tickPositions;
    tickPositions.forEach(pos => {
        const tick = axis.ticks[pos];
        if (tick.label?.element) { // ❌ Crashes if tick is undefined

// After
if (axis.ticks && axis.tickPositions) {
    const tickPositions = axis.tickPositions;
    tickPositions.forEach(pos => {
        const tick = axis.ticks[pos];
        if (tick && tick.label?.element) { // ✅ Safe

Demo where issue is visible in browser console:
https://jsfiddle.net/241fkqr6/

Impact:
This fix ensures the plugin works correctly with Sankey charts and other chart types that don't have traditional axes, while maintaining backward compatibility with all existing chart types.

[PaultjeScholes]

@FadhlurZ Can we add a label Type: Bug and perhaps add reviewers to get this merged, we are running into the same issue

[FadhlurZ]

@PaultjeScholes Unfortunately it looks like I am not able to add reviewers and a label to this PR. Could you @K009 @mfilipiec maybe take a look at this PR? I think it has quite a big impact for some users of this package.

[K009]

Hi, thanks a lot for your contribution and for catching this bug. The fix looks solid, happy to merge!