fix(tooltip): guard against removed series in cached axis tooltip params (Fixes #21732)

[waterWang]

Fixes #21732

Problem

TooltipView._showAxisTooltip iterates axisItem.seriesDataIndices whose seriesIndex values come from the cached pointer state (_lastDataByCoordSys). When a merged setOption removes series (e.g. replaceMerge: ['series', ...]) while the tooltip is still showing, those cached indices become stale and ecModel.getSeriesByIndex(idxItem.seriesIndex) returns undefined, causing:

Uncaught TypeError: Cannot read properties of undefined (reading 'getDataParams')
    at TooltipView._showAxisTooltip

Root cause

1. TooltipView caches the last hovered pointer state in _lastX / _lastY / _lastDataByCoordSys.
2. Every setOption runs TooltipView.render() → _keepShow(), which re-shows the tooltip with the cached dataByCoordSys after the update.
3. The new option has fewer series than the cached indices refer to → getSeriesByIndex returns undefined → series.getDataParams(...) throws.

Fix

Two defensive guards in _showAxisTooltip:

1. Skip stale seriesDataIndices entries whose series no longer exists: if (!series) { return; }
2. Move the existing !axisModel guard before the axisModel.axis access (it was previously checked after being dereferenced), so a removed axis also short-circuits instead of crashing.

Test

With tooltip: {trigger: 'axis'}, hover to show the tooltip, then setOption with fewer series in merge mode — the tooltip no longer throws and safely skips removed series.

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