Fix a dig segfault due to bad linked list usage [RT #37591]

The crash (#37591) seems to happen because the query is taken out of
lookup->q(query->link), and put on lookup->connecting(query->clink).
The code checks query->link where it is detached (-1 in next pointer).
However, there's no need to call send_tcp_connect() there as the queries
are already connecting at that point.

CHANGES

+4016.	[bug]		Fix a dig segfault due to bad linked list usage.
+			[RT #37591]
+
 4015.	[bug]		Nameservers that are skipped due to them being
 			CNAMEs were not being logged. They are now logged
 			to category 'cname' as per BIND 8. [RT #37935]

bin/dig/dighost.c

@@ -3242,7 +3242,8 @@ connect_done(isc_task_t *task, isc_event_t *event) {
 		query->waiting_connect = ISC_FALSE;
 		isc_event_free(&event);
 		l = query->lookup;
-		if (l->current_query != NULL)
+		if ((l->current_query != NULL) &&
+		    (ISC_LINK_LINKED(l->current_query, link)))
 			next = ISC_LIST_NEXT(l->current_query, link);
 		else
 			next = NULL;