Bug: Getting NXDOMAIN when not expected

[mageddo]

Reported at #478

What is Happening

DPS solvers are forwarding the hostname query to remote solver even when the hostname exists at the dps solvers but haven´t an IP to be answered, then it causes a NXDOMAIN answer got from the remote solver or by the MG_NO_ENTRIES_RESPONSE_CODE when no remote solver could be used.

What is Expected

As explained by @aricooperdavis (ref), following the RFCs, the expected behavior would be:

• if the domain exists in any solver then that solver should handle the response.
• if a record of the requested type doesn't exist under that solver then it should return RCODE 0 ("No Error"/"NODATA").

Here are the relevant RFC standards:

• RFC 1035 states that the "Name Error" RCODE (i.e. 3, "NXDOMAIN") >"signifies that the domain name referenced in the query does not exist".
• RFC 2308 clarifies that the more appropriate RCODE would be "No Error" (i.e. 0, >"NODATA"), "which indicates that the name is valid, for the given class, but [there] are no records of the given type.".