A crash was caused by an incorrect timer handler nxt_h1p_idle_timeout() if
SSL_shutdown() returned SSL_ERROR_WANT_READ/SSL_ERROR_WANT_WRITE.
The flag SSL_RECEIVED_SHUTDOWN is used to avoid getting SSL_ERROR_WANT_READ, so
the server won't wait for a close notification from a client.
For SSL_ERROR_WANT_WRITE, a correct timer handler is set up.
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