RFC 6120 §8.1.2.1: a stanza received over a c2s stream without a 'from'
attribute must be treated as coming from the server itself. The
on-connect disco#info handler passed the absent attribute as NULL into
connection_features_received(), where g_str_hash() dereferenced the NULL
key and crashed (remotely triggerable DoS on connect).
Substitute connection_get_domain() at both disco#info handler
boundaries, and make connection_features_received() and
connection_get_features() NULL-safe as defense in depth. Add a stabber
regression test answering the on-connect disco#info with a from-less
result.
Fixes#168
Add 7 new tests for /disco command:
- disco_items_to_jid: query items to specific JID
- disco_info_empty_result: handle empty disco#info response
- disco_info_multiple_identities: multiple identity elements
- disco_info_without_name: identity without optional name attr
- disco_items_without_name: items without optional name attr
- disco_info_service_unavailable: error handling for info
- disco_items_error_handling: error handling for items (XEP-0030 §7)
The disco_items_error_handling test documents a bug where disco#items
errors are silently ignored (unlike disco#info which handles them).
This violates XEP-0030 Section 7 which requires error feedback to user.
- Add 8 tests for disco info and disco items commands
- Fix XEP-0030 compliance bug: show message for empty disco#items results
- Tests cover: identity display, features, server/jid queries, error handling,
items display, empty results, and connection requirement
