Shadowserver parser: Bad error message if report name is unknown

[ghost]

If the report has not file name then this exception occurs:

Bot has found a problem.
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/dist-packages/intelmq/lib/bot.py", line 267, in start
    self.process()
  File "/usr/local/lib/python3.6/dist-packages/intelmq/lib/bot.py", line 942, in process
    for line in self.parse(report):
  File "/usr/local/lib/python3.6/dist-packages/intelmq/bots/parsers/shadowserver/parser.py", line 65, in parse
    filename_search = self.__is_filename_regex.search(self.report_name)
TypeError: expected string or bytes-like object

Should be a human readable error message.