Reset current_hostgroup to default when no query rule matches

In the extended query protocol flow (Parse/Bind/Execute/Sync messages), queries without matching query rules were incorrectly retaining the current_hostgroup value from the previous query instead of being reset to the default_hostgroup.

This happened because:
  - Simple query protocol goes through STATE_SLEEP between queries, which
    resets current_hostgroup to default_hostgroup
  - Extended query protocol does NOT go through STATE_SLEEP between
    Parse/Bind/Execute messages, so current_hostgroup was never reset

lib/PgSQL_Session.cpp

@@ -4470,8 +4470,13 @@ __exit_set_destination_hostgroup:
 		next_query_flagIN = qpo->next_query_flagIN;
 	}
 
-	if (qpo->destination_hostgroup >= 0 && transaction_persistent_hostgroup == -1) {
-		current_hostgroup = qpo->destination_hostgroup;
+	if (transaction_persistent_hostgroup == -1) {
+		if (qpo->destination_hostgroup >= 0) {
+			current_hostgroup = qpo->destination_hostgroup;
+		} else {
+			// No query rule matched - use default hostgroup
+			current_hostgroup = default_hostgroup;
+		}
 	}
 
 	// Hostgroup locking check