ids-functions.pl: Try to enumerate the dl_rulesfile if a provider is not

ids-functions.pl: Try to enumerate the dl_rulesfile if a provider is not
supported anymore.

In this case the details about the file suffix is not available in the
ruleset-sources file anymore. In this case now the function tries to
enumerate the correct filename.

This allows to display the correct stats in the WUI and to extract and
use the downloaded ruleset of the provider until it got deleted by the
user.

Signed-off-by: Stefan Schantl <stefan.schantl@ipfire.org>