[RPC] Fix for non-rpc users (#4143)

* [RPC] Fix for non-rpc users

  - RPC probably needs rewriting.
  - Also, I noticed some extremely sharp edges
  and a potential crash point (unrelated to the fixed issue)
  on windows that the side effects from have been mitigated here
  partially.

* sysexit on initialization failure

redbot/core/bot.py

@@ -1370,7 +1370,8 @@ class RedBase(
         await super().logout()
         await drivers.get_driver_class().teardown()
         try:
-            await self.rpc.close()
+            if self.rpc_enabled:
+                await self.rpc.close()
         except AttributeError:
             pass