[instagram] Fix for missing edge_media_to_comment' field and add date' metadata

[iamleot]

Probably since last hours/days (at least the CI has not spotted
that problem yet) the edge_media_to_comment' field is not always present in the sharedData JSON. Sometimes it is present in the response, other times not, also for the same URL. Previously, the count' field of edge_media_to_comment' was used to populate comments' metadata with the number of comments.
For completeness a complete test showing such error will be added
at the end of this pull request.

Add date' metadata using taken_at_timestamp' field.

Here the complete output of the failing tests:

% env PYTHONPATH=. python3.7 test/test_results.py instagram

https://www.instagram.com/p/BqvsDleB3lV/
.
https://www.instagram.com/p/BoHk1haB5tM/
E
https://www.instagram.com/p/Bqxp0VSBgJg/
.
https://www.instagram.com/p/BtOvDOfhvRr/
.
https://www.instagram.com/explore/tags/instagram/
E
https://www.instagram.com/instagram/
.
======================================================================
ERROR: test_InstagramImageExtractor_2 (__main__.TestExtractorResults)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test/test_results.py", line 258, in test
    self._run_test(extr, url, result)
  File "test/test_results.py", line 61, in _run_test
    tjob.run()
  File "test/test_results.py", line 152, in run
    for msg in self.extractor:
  File ".../gallery-dl/gallery_dl/extractor/instagram.py", line 32, in items
    for data in self.instagrams():
  File ".../gallery-dl/gallery_dl/extractor/instagram.py", line 232, in instagrams
    return self._extract_postpage(url)
  File ".../gallery-dl/gallery_dl/extractor/instagram.py", line 53, in _extract_postpage
    'comments': text.parse_int(media['edge_media_to_comment']['count']),
KeyError: 'edge_media_to_comment'

======================================================================
ERROR: test_InstagramTagExtractor_1 (__main__.TestExtractorResults)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test/test_results.py", line 258, in test
    self._run_test(extr, url, result)
  File "test/test_results.py", line 61, in _run_test
    tjob.run()
  File "test/test_results.py", line 152, in run
    for msg in self.extractor:
  File ".../gallery-dl/gallery_dl/extractor/instagram.py", line 32, in items
    for data in self.instagrams():
  File ".../gallery-dl/gallery_dl/extractor/instagram.py", line 162, in _extract_tagpage
    yield from self._extract_page(url, 'TagPage')
  File ".../gallery-dl/gallery_dl/extractor/instagram.py", line 135, in _extract_page
    yield from self._extract_postpage(url)
  File ".../gallery-dl/gallery_dl/extractor/instagram.py", line 53, in _extract_postpage
    'comments': text.parse_int(media['edge_media_to_comment']['count']),
KeyError: 'edge_media_to_comment'

----------------------------------------------------------------------
Ran 6 tests in 11.946s

FAILED (errors=2)

[mikf]

Thank you!

[iamleot]

Mike Fährmann writes:

Thank you!

Thank you Mike for quickly applying them!