Fix the validate of form should pass extra_validators (#547)

Co-authored-by: jwag956 <jwag.wagner@gmail.com>
Co-authored-by: chlrlrhs95 <chlrlrhs95@naver.com>

src/flask_wtf/form.py

@@ -83,7 +83,7 @@ def validate_on_submit(self, extra_validators=None):
         """Call :meth:`validate` only if the form is submitted.
         This is a shortcut for ``form.is_submitted() and form.validate()``.
         """
-        return self.is_submitted() and self.validate(extra_validators)
+        return self.is_submitted() and self.validate(extra_validators=extra_validators)
 
     def hidden_tag(self, *fields):
         """Render the form's hidden fields in one call.