[Instagram] Add support for user's saved collection

[sheeyang]

This adds support for user's saved collection medias, previously it would just download the user's entire saved medias.

[mikf]

Thanks for the PR.

I seem to be unable to push any changes regarding this PR to your branch, so please apply this patch yourself:

diff --git a/gallery_dl/extractor/instagram.py b/gallery_dl/extractor/instagram.py
index f6f76eee..8f179113 100644
--- a/gallery_dl/extractor/instagram.py
+++ b/gallery_dl/extractor/instagram.py
@@ -526,11 +526,19 @@ class InstagramCollectionExtractor(InstagramExtractor):
         "https://www.instagram.com/instagram/saved/collection_name/123456789/",
     )
 
+    def __init__(self, match):
+        InstagramExtractor.__init__(self, match)
+        self.user, self.collection_name, self.collection_id = match.groups()
+
+    def metadata(self):
+        return {
+            "collection_id"  : self.collection_id,
+            "collection_name": text.unescape(self.collection_name),
+        }
+
     def posts(self):
-        collection_id = self.url.split(
-            "/")[-2] if self.url[-1] == "/" else self.url.split("/")[-1]
-        endpoint = "/v1/feed/collection/{}/posts/".format(collection_id)
-        for item in self._pagination_api(endpoint, {}):
+        endpoint = "/v1/feed/collection/{}/posts/".format(self.collection_id)
+        for item in self._pagination_api(endpoint):
             yield item["media"]

It simplifies the 'collection_id' retrieval and adds some useful metadata fields. You should also run make (or scripts/supportedsites.py) to updated the list of supported sites.

[sheeyang]

Thank you, I applied the patch and gave you write access to the branch.

[sheeyang]

I should mention I changed the None to {} here to prevent this error when the collection has more available

[instagram][error] An unexpected error occurred: TypeError - 'NoneType' object does not support item assignment. Please run gallery-dl again with the --verbose flag, copy its output and report this issue on https://github.com/mikf/gallery-dl/issues .
[instagram][debug]
Traceback (most recent call last):
  File "/mnt/d/REPO/PUBLIC/gallery-dl/gallery_dl/job.py", line 77, in run
    for msg in extractor:
  File "/mnt/d/REPO/PUBLIC/gallery-dl/gallery_dl/extractor/instagram.py", line 49, in items
    for post in self.posts():
  File "/mnt/d/REPO/PUBLIC/gallery-dl/gallery_dl/extractor/instagram.py", line 541, in posts
    for item in self._pagination_api(endpoint):
  File "/mnt/d/REPO/PUBLIC/gallery-dl/gallery_dl/extractor/instagram.py", line 408, in _pagination_api
    params["max_id"] = data["next_max_id"]
TypeError: 'NoneType' object does not support item assignment