touchMove crashes with "Cannot read properties of null (reading 'offsetWidth')" when the current slide element is not in the DOM

Description

touchMove throws TypeError: Cannot read properties of null (reading 'offsetWidth') when the current slide element isn't in the DOM at the moment of a drag/swipe.

Note that on desktop this is reached via mouse drag, not touch: the enableDrag handler binds mousemove on window and calls touchMove (lib/lightgallery.js, ~line 1446), and the touch enableSwipe handler calls it too (~line 1384). In touchMove the current slide width is read unconditionally:

  const $currentSlide = this.getSlideItem(this.index);
  if (this.swipeDirection === 'horizontal') {
      e?.preventDefault();
      this.outer.addClass('lg-dragging');
      this.setTranslate($currentSlide, distanceX, 0);
      const width = $currentSlide.get().offsetWidth; //  $currentSlide.get() is null
      ...
  }

Steps to reproduce

Timing/race condition, so intermittent rather than 100% reproducible, but it shows up consistently in our error tracking. Captured on desktop (macOS + Chrome) via mouse drag:

1. Initialize in dynamic mode with mode: 'lg-fade' and speed: 0 (config below).
2. Open the gallery and start dragging a slide horizontally with the mouse.
3. While dragging, the current slide item leaves the DOM (dynamic (re)build / slide change), but the window-bound mousemove keeps calling touchMove.
4. getSlideItem(this.index).get() returns null → TypeError on .offsetWidth.

(No public demo, it happens on an internal admin page. Can provide more detail from the captured events.)

JS code that you use to initialize lightGallery.

  lightGallery(container, {
      speed: 0,
      mode: 'lg-fade',
      slideEndAnimation: false,
      closeOnTap: false,
      startAnimationDuration: 0,
      startClass: '',
      preload: 4,
      mousewheel: true,
      actualSize: false,
      showZoomInOutIcons: true,
      infiniteZoom: true,
      plugins: [lgThumbnail, lgZoom, lgFullscreen, lgRotate],
      dynamic: true,
      dynamicEl: [
          { src: 'img/img1.jpg', thumb: 'img/thumb1.jpg', subHtml: '' },
          { src: 'img/img2.jpg', thumb: 'img/thumb2.jpg', subHtml: '' },
          // ...
      ],
      escKey: false,
      licenseKey: '1',
      flipHorizontal: false,
      flipVertical: false,
      download: false,
      mobileSettings: {
          showCloseIcon: true,
          download: false,
          rotate: false,
      },
  });

Sample HTML markup

  <!-- dynamic mode: items are provided via dynamicEl, the container is empty -->
  <div id="lightgallery"></div>

Environment

• Browser and version - Chrome 150 (desktop)
• OS - macOS (Mac OS X >= 10.15.7)
• lightGallery version - 2.8.3 (the offending line is unchanged in 2.9.0 as well)

Additional context

• Reproduced on desktop via mouse drag (enableDrag); the same code path is also reachable via touch swipe (enableSwipe).
• User-facing impact is negligible (at worst one stuttering drag frame; navigation still completes on mouseup/touchend), but it produces recurring uncaught exceptions in our error tracking.
• The mousemove drag listener is bound to window, so it keeps invoking touchMove after the drag starts even if the current slide element is removed/replaced.