fix bad_variant_access resulting from ConvoTag->AddressVariant change

We changed the quic code to refer to its remote endpoint using an Address Variant
and this resulted in a crash when sending a connection close packet.  This code was
incorrectly supplying an uninitialized value for ConvoTag before but this was silently
ignored; after switching to a variant it became a crash.

llarp/quic/endpoint.cpp

@@ -295,11 +295,10 @@ namespace llarp::quic
         close_reason.size());
 
     conn.conn_buffer.resize(max_pkt_size_v4);
-    Path path;
     ngtcp2_pkt_info pi;
 
     auto written = ngtcp2_conn_write_connection_close(
-        conn, path, &pi, u8data(conn.conn_buffer), conn.conn_buffer.size(), &err, get_timestamp());
+        conn, &conn.path.path, &pi, u8data(conn.conn_buffer), conn.conn_buffer.size(), &err, get_timestamp());
     if (written <= 0)
     {
       log::warning(
@@ -314,8 +313,6 @@ namespace llarp::quic
     conn.conn_buffer.resize(written);
     conn.closing = true;
 
-    conn.path = path;
-
     assert(conn.closing && !conn.conn_buffer.empty());
 
     if (auto sent = send_packet(conn.path.remote, conn.conn_buffer, 0); not sent)
@@ -411,6 +408,7 @@ namespace llarp::quic
     conns.erase(it);
     if (primary)
       clean_alias_conns();
+
     return true;
   }