Record changes to stream list sooner

We used to wait until all work in the admission webhook was done to save
out the new list of streams as edited by the webhook. This produces two
issues:

1. It was possible to encounter a race condition if a second webhook
fired while the first was still processing the callout to Discord
2. If the webhook throttle engaged, `handle_notify()` would return
before saving the list out at all

Now we inspect the list, decide what we're going to do, save the new
list out, and then call the Discord webhook as appropriate.

admission.py

@@ -85,8 +85,15 @@ def handle_notify() -> None:
     if not cherrypy.request.update_opening and cherrypy.request.update_stream in stream_list:
         stream_list.remove(cherrypy.request.update_stream)
 
-    # If we haven't gone empty->active or active->empty we need to do nothing
-    if bool(stream_list) != bool(config.LAST_STREAM_LIST):
+    # Figure out if we changed state between "someone online" and "no one online"
+    changed = bool(stream_list) != bool(config.LAST_STREAM_LIST)
+
+    # Save our stream list out before dispatching any webhooks
+    # We do this before any network callouts to try to prevent race conditions
+    # FIXME: The right way to handle this is threadsafe locking
+    config.LAST_STREAM_LIST = stream_list.copy()
+
+    if changed:
         if not check_webhook_throttle():
             cherrypy.log("Webhook throttle limit hit, ignoring")
             return
@@ -94,10 +101,6 @@ def handle_notify() -> None:
         # Dispatch the appropriate webhook
         webhook_online(stream_list[0]) if stream_list else webhook_offline()
 
-    # Save our stream list into a durable value
-    cherrypy.log(str(stream_list))
-    config.LAST_STREAM_LIST = stream_list.copy()
-
 
 class Admission:
     # /admission to control/trigger sessions