fix(validators): Disabled validation with provided formdata

[subnix]

The Field.raw_data attribute has three states:

1. None: The form data hasn't been passed.
2. A list with a single value: The form data has been passed, and the field is present.
3. An empty list: The form data has been passed, but the field is missing.

wtforms/src/wtforms/fields/core.py

Line 21 in 7477295

raw_data = None

wtforms/src/wtforms/fields/core.py

Lines 313 to 317 in 7477295

	if formdata is not None:
	if self.name in formdata:
	self.raw_data = formdata.getlist(self.name)
	else:
	self.raw_data = []

Currently, the validator correctly supports the first two states (passes the validation and fails, respectively). However, it should also support the third state, which should pass the validation.

Relates to #792 #797

[azmeuk]

Thank you for your contribution!