For Enterprise Grid workspaces with xoxc/xoxd session tokens, the
server exclusively used the edge API for channel listing. If the
edge API returned an error, the server propagated it with no
channels.
Add a fallback to the standard conversations.list API, which also
works with xoxc tokens in many Enterprise Grid setups. Cache the
edge failure in an edgeFailed flag so that subsequent pagination
calls go straight to the standard API instead of retrying and
failing on every page.
George Bashi