QUIC: removed excessive check.

QUIC: removed excessive check.

The c->udp->dgram may be NULL only if the quic connection was just
created: the ngx_event_udp_recvmsg() passes information about datagrams
to existing connections by providing information in c->udp.

If case of a new connection, c->udp is allocated by the QUIC code during
creation of quic connection (it uses c->sockaddr to initialize qsock->path).

Thus the check for qsock->path is excessive and can be read wrong, assuming
that other options possible, leading to warnings from clang static analyzer.