Describe the bug

My Prosody XMPP server, which uses libunbound, can't do outgoing DNS since updating to 1.18.0.

To reproduce
Steps to reproduce the behavior:

1. Build libunbound with nettle
2. Run prosody

Expected behavior
Prosody could make DNS requests, and send outgoing messages.

System:

• Unbound version: 1.18.0
• OS: NixOS
• unbound -V output: n/a; built with --with-libunbound-only

Additional information

Bisected to 7e6a7f3.

From inspection, it appears that, since connect_sslctx_create returns null if built without OpenSSL, setup will now always fail.