Fix crash after re-reading an empty resolv.conf file.
If dnsmasq re-reads a resolv file, and it's empty, it will
retry after a delay. In the meantime, the old servers from the
resolv file have been deleted, but the servers_array doesn't
get updated, leading to dangling pointers and crashes.
Thanks to Brad Jorsch for finding and analysing this bug.
Fix confusion is server=/domain/# combined with server|address=/domain/....
The 2.86 domain matching rewrite failed to take into account the possibilty that
server=/example.com/#
could be combined with, for example
address=/example.com/1.2.3.4
resulting in the struct server datastructure for the former getting passed
to forward_query(), rapidly followed by a SEGV.
This fix makes server=/example.com/# a fully fledged member of the
priority list, which is now IPv6 addr, IPv4 addr, all zero return,
resolvconf servers, upstream servers, no-data return
Thanks to <email address hidden> for finding and characterising the bug.