Added an .empty() function to the objects, fixes to msgs_ack

The .empty() function returns an "empty" instance of the object
(attributes set to None). This is used rather than using reflection.

The msgs_ack handling broke stuff (InvokeWithLayer when there were
updates), so this is now handled; yet there may be a better fix

telethon/utils/binary_reader.py

@@ -117,14 +117,9 @@ class BinaryReader:
             # If there was still no luck, give up
             raise TypeNotFoundError(constructor_id)
 
-        # Now we need to determine the number of parameters of the class, so we can
-        # instantiate it with all of them set to None, and still, no need to write
-        # the default =None in all the classes, thus forcing the user to provide a real value
-        sig = inspect.signature(clazz.__init__)
-        params = [None] * (len(sig.parameters) - 1)  # Subtract 1 (self)
-        result = clazz(*params)  # https://docs.python.org/3/tutorial/controlflow.html#unpacking-argument-lists
-
-        # Finally, read the object and return the result
+        # Create an empty instance of the class and
+        # fill it with the read attributes
+        result = clazz.empty()
         result.on_response(self)
         return result