Error when initializing virtual list with defined scrollToIndex

[mskocik]

When property scrollToIndex has value, it result in following error. See REPL

can't access lexical declaration 'state' before initialization

This is due initialization check not expecting scrollToIndex can have initial value;

Fix is easy - add check also for items.length for state.offset initialization:

// VirtualList.svelte: 62
let state = {
  offset:             scrollOffset || (scrollToIndex != null && items.length && getOffsetForIndex(scrollToIndex)) || 0,
  scrollChangeReason: SCROLL_CHANGE_REASON.REQUESTED,
};