Ed448: check for public key presence on export #585

Job	Run time
smoke (leantls-extra, --enable-leantls --enable-session-ticket --enable-sni --enable-opensslextra)	1m 45s
smoke (cryptonly, --enable-cryptonly)	1m 43s
smoke (enable-all-smallstack, --enable-all --enable-smallstack)	4m 12s
smoke (sanitize-asan, --enable-all, -fsanitize=address -fno-omit-frame-pointer -g -O1, -fsanitize...	4m 53s
smoke (dtls-suite, --enable-psk --enable-dtls --enable-dtls13 --enable-dtls-mtu --enable-aesccm -...	2m 39s
smoke (enable-all, --enable-all)	4m 8s
smoke (opensslextra, --enable-opensslextra)	2m 23s
smoke (default)	2m 21s
smoke (integration, --enable-openssh --enable-lighty --enable-stunnel --enable-opensslextra)	3m 13s
	27m 17s

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