fix: skip y-axis band when selected overlay has no point values

[NemeZZiZZ]

Problem

OverlayYAxisView paints the selected overlay's band rect from topY/bottomY, which start as Number.MAX_SAFE_INTEGER / Number.MIN_SAFE_INTEGER and are updated only for points that carry a numeric value:

let topY = Number.MAX_SAFE_INTEGER
let bottomY = Number.MIN_SAFE_INTEGER
coordinates.forEach((coordinate, index) => {
  const point = overlay.points[index]
  if (isNumber(point.value)) { topY = …; bottomY = …; … }
})
if (coordinates.length > 1) {
  figures.unshift({ type: 'rect', attrs: { x: 0, y: topY, height: bottomY - topY, … } })
}

For an overlay whose points carry only timestamp (e.g. verticalSegment, verticalRayLine) created programmatically — createOverlay({ name: 'verticalSegment', points: [{ timestamp: a }, { timestamp: b }] }) — and then selected by click, no point has a value, so the rect is emitted with y ≈ 9e15 and height ≈ -1.8e16: a fill covering the entire y-axis widget.

(UI drawing is not affected — _coordinateToPoint always sets value there; the trigger is programmatic points without value, plus selection, since the band renders only for the clicked overlay.)

Fix

Emit the band only when at least one point actually contributed: topY <= bottomY is true iff the loop updated the sentinels. One condition added.