Handle empty DNS reply without error as NOERROR

This re-introduces an error code to handle returning empty DNS replies instead of sending NXDOMAIN error, which fixes resolving IPv6 only destinations when first sending an A type DNS request, as most applications do. As discussed in #40984 (closed) the previous commit was reverted. This is the exact same code as the previously merged one, but as suggested in the issue uses an error code outside the 0-255 range, which is safe for internal use in the C Tor implementation. Fixes #40248