Purger: If active member has already left the server, the purger errors

[Maelstromeous]

What's happening is if someone has left the active members list, the Discord function to get them will fail. We need to allow it to fail, and simply remove the member from the active list.

[Maelstromeous]

Should never occur as of bc4a5a3, because whenenever someone leaves their record should be removed along with it.

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