onBeforeClip exceptions leave the scroller inconsistent and busy #87

Problem

settings.onBeforeClip is called after rows are hidden and virtual padding is updated, but before their items are removed from the Buffer.

If the callback throws, clipping stops midway: the rendered list and Buffer become inconsistent, the workflow cycle remains busy, and adapter.relax() may never resolve.

Reproduction

1. Initialize a scroller with settings.infinite: true.
2. Scroll far enough to accumulate rows outside the visible area.
3. Configure onBeforeClip to throw an exception.
4. Call adapter.clip().

Clipping does not complete, and the scroller remains busy.

The same problem can occur during automatic clipping.

Expected

An exception from onBeforeClip must not leave clipping incomplete or the scroller stuck:

• Finish clipping and any required viewport adjustment.
• Finalize the cycle and restore consistent DOM/Buffer state.
• Preserve and rethrow the original exception, including throw undefined.
• Allow subsequent scrolling and Adapter operations to continue.
• Do not lose a pending exception if the scroller is disposed before its deferred rethrow.