Fixed #1756 -- Permit selecting no file in a FilePathField with blank = True.

    "A SelectField whose choices are the files in a given directory."

    def __init__(self, field_name, path, match=None, recursive=False, is_required=False, validator_list=None):

        import os

        from django.db.models import BLANK_CHOICE_DASH

        if match is not None:

            import re

            match_re = re.compile(match)

        choices = []

        choices = not is_required and BLANK_CHOICE_DASH[:] or []

        if recursive:

            for root, dirs, files in os.walk(path):

                for f in files: