general-functions.pl: Fix for bug#12937

general-functions.pl: Fix for bug#12937

- The check for validwildcarddomainname did not allow wildcards of the form
   *.ipfire.org* which is the example given on the proxy.cgi page for excluded url's
   for the wpad file.
- A forum user sufferred from this problem and the bug was raised for it.
   https://community.ipfire.org/t/proxy-cgi-error-message-when-use-wildcard-in-wpad-excluded-url-s/8597
   forum user has tested the patch change and confirmed it solves the problem.

Fixes: Bug#12937
Suggested-by: Bernhard Bitsch <bbitsch@ipfire.org>
Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Reviewed-by: Bernhard Bitsch <bbitsch@ipfire.org>