Fix patched module was never automatically imported

Closes #1701. It has to be imported late in the process of
`import telethon` for its side-effects.

telethon/__init__.py

@@ -2,6 +2,7 @@
 from .network import connection
 from .tl import types, functions, custom
 from .tl.custom import Button
+from .tl import patched as _  # import for its side-effects
 from . import version, events, utils, errors
 
 __version__ = version.__version__