Add a variable to fetch the latest snapshot only

[vladkvit]

Returns only the latest snapshot within the provided time range.

[shanept]

Line 197 throws an error if filtered_snapshots is an empty array:

2024-02-17 22:29:46 [scrapy.core.scraper] ERROR: Error downloading <GET https://web.archive.org/cdx/search/cdx?url=https%3A//kcg.wikipedia.org/&output=json&fl=timestamp,original,statuscode,digest>
Traceback (most recent call last):
  File "/home/shane/.local/lib/python3.8/site-packages/twisted/internet/defer.py", line 2000, in _inlineCallbacks
    result = context.run(gen.send, result)
  File "/home/shane/.local/lib/python3.8/site-packages/scrapy/core/downloader/middleware.py", line 68, in process_response
    method(request=request, response=response, spider=spider)
  File "/home/shane/.local/lib/python3.8/site-packages/scrapy_wayback_machine/__init__.py", line 77, in process_response
    snapshot_requests = self.build_snapshot_requests(response, meta)
  File "/home/shane/.local/lib/python3.8/site-packages/scrapy_wayback_machine/__init__.py", line 134, in build_snapshot_requests
    for snapshot in self.filter_snapshots(snapshots):
  File "/home/shane/.local/lib/python3.8/site-packages/scrapy_wayback_machine/__init__.py", line 197, in filter_snapshots
    return [filtered_snapshots[-1]]
IndexError: list index out of range

Suggest modifying slightly. The following works well for me:

if self.fetch_latest_only and len(filtered_snapshots):
    return [filtered_snapshots[-1]]
else:
    return filtered_snapshots