Fix module reloading incorrectly on exception (#295)

* Restores old module in Bot._modules dict explicitly on exception

* Update changelog

Author: SigmathBits

docs/changelog.rst

@@ -11,6 +11,7 @@ Massive documentation updates
 - ext.commands
     - :func:`Bot.handle_commands` now also invokes on threads / replies
     - Cooldowns are now handled correctly per bucket.
+    - Fix issue with :func:`Bot.reload_module` where module is reloaded incorrectly if exception occurs
 
 - ext.pubsub
     - Channel subscription model fixes.

twitchio/ext/commands/bot.py

@@ -441,6 +441,7 @@ def reload_module(self, name: str):
         except Exception as e:
             sys.modules.update(modules)
             module.prepare(self)  # type: ignore
+            self._modules[name] = module
             raise
 
     def add_cog(self, cog: Cog):