Fixed not updating last_spoke when we should have.

diff --git a/bot.py b/bot.py
index 6aa17f0..bd016b6 100755 (executable)
--- a/bot.py
+++ b/bot.py
@@ -1599,7 +1599,8 @@ def announce(announcement):
         else:
           log.info("Didn't bother with announcement {}".format(announcement['id']))
       # Set last_spoke even if we chose not to announce.
-      update['digest'] = digest
+      if digest is not None:
+        update['digest'] = digest
       db.update_announcement(client, announcement['id'], **update)
       if not announce:
         return