github.lister: Filter out partial repositories which break listing

This commit fixes the repository mapping to model. It broke when the listed
repository was either None or missing the id field [1]

[1] https://sentry.softwareheritage.org/share/issue/532d682182fc43d6a7a99400e3928811/

swh/lister/github/lister.py

@@ -49,7 +49,8 @@ class GitHubLister(IndexingHttpLister):
 
     def transport_response_simplified(self, response):
         repos = response.json()
-        return [self.get_model_from_repo(repo) for repo in repos]
+        return [self.get_model_from_repo(repo)
+                for repo in repos if repo and 'id' in repo]
 
     def request_headers(self):
         """(Override) Set requests headers to send when querying the GitHub API

swh/lister/github/tests/data/https_api.github.com/repositories,since=0

@@ -66,6 +66,10 @@
     "releases_url": "https://api.github.com/repos/mojombo/grit/releases{/id}",
     "deployments_url": "https://api.github.com/repos/mojombo/grit/deployments"
   },
+  {
+    "description": "Azure Qu..."
+  },
+  {},
   {
     "id": 26,
     "node_id": "MDEwOlJlcG9zaXRvcnkyNg==",