location-importer.in: Fix dangling variable

location-importer.in: Fix dangling variable

This fixes:

Traceback (most recent call last):
  File "/usr/bin/location-importer", line 1607, in <module>
    main()
  File "/usr/bin/location-importer", line 1605, in main
    c.run()
  File "/usr/bin/location-importer", line 140, in run
    ret = args.func(args)
  File "/usr/bin/location-importer", line 1234, in handle_update_overrides
    self._update_overrides_for_spamhaus_drop()
  File "/usr/bin/location-importer", line 1504, in _update_overrides_for_spamhaus_drop
    for sline in t.readlines():
NameError: name 't' is not defined

Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>