FieldList.last_index isn't reset in the .process() method

[Tyler-Petrov]

In the FieldList.proccess() method the .entries property is set to an empty string, but .last_index isn't reset to -1. I'm assuming this isn't correct. This would be line 71 in fields/list.py.

In my code I need to call FieldList.process() multiple times, and that messes with what's stored in the entries list.

Here's some pseudo code to get the idea across:

class NameForm(Form):
    first = StringField()
    last = StringField()


class UserForm(Form):

    test_forms = FieldList(FormField(NameForm), min_entries=3)


user_form = UserForm()

# These lead to .last_index and .entries not being synced
user_form.test_forms.process(...)
user_form.test_forms.process(...)
user_form.test_forms.process(...)

Love the module by the way! It's really my bread and butter.