Fix a bug where None would be returned in try_owners if the cache wasn't yet ready.

discord/ext/commands/bot.py

@@ -381,6 +381,10 @@ class BotBase(GroupMixin):
                 if owner:
                     owners.append(owner)
             return owners
+        else:
+            # We didn't have owners cached yet, cache them and retry.
+            await self.populate_owners()
+            return await self.try_owners()
 
     async def populate_owners(self):
         """|coro|