fix broken windows build

The MSVS C compiler requires every struct to have at least one member. The dns_geoip_databases_t structure had one set of members for HAVE_GEOIP and a different set for HAVE_GEOIP2, and none when neither API is in use.

This commit silences the compiler error by moving the members that were in common between the two versions of the structure (isp, as, and domain) outside of the #ifdef.

Closes #1114 (closed)