[commands] Unload cog when command registration fails in _inject

discord/ext/commands/cog.py

@@ -459,6 +459,9 @@ class Cog(metaclass=CogMeta):
                     for to_undo in self.__cog_commands__[:index]:
                         if to_undo.parent is None:
                             bot.remove_command(to_undo.name)
+                    try:
+                        await maybe_coroutine(self.cog_unload)
+                    finally:
                         raise e
 
         # check if we're overriding the default