Also check arg count in weak mode.

Author: Guido van Rossum

mypy/checkexpr.py

@@ -238,7 +238,7 @@ def check_call(self, callee: Type, args: List[Node],
             arg_types = self.infer_arg_types_in_context2(
                 callee, args, arg_kinds, formal_to_actual)
 
-            if self.chk.typing_mode_full():
+            if not self.chk.typing_mode_none():
                 self.check_argument_count(callee, arg_types, arg_kinds,
                                           arg_names, formal_to_actual, context, self.msg)