APPS/pkcs8: fix case where infile and outfile are the same #1441

Job	Run time
run-checker (no-cmp)	5m 13s
run-checker (no-cms)	5m 13s
run-checker (no-dgram)	4m 51s
run-checker (no-dh)	5m 18s
run-checker (no-dtls)	5m 38s
run-checker (no-ec)	5m 33s
run-checker (no-ecx)	5m 12s
run-checker (no-http)	5m 38s
run-checker (no-legacy)	5m 26s
run-checker (no-sock)	4m 47s
run-checker (enable-ssl-trace)	5m 21s
run-checker (no-stdio)	2m 35s
run-checker (no-threads)	5m 2s
run-checker (no-thread-pool)	5m 18s
run-checker (no-default-thread-pool)	5m 28s
run-checker (no-tls)	4m 40s
run-checker (no-tls1_2)	5m 7s
run-checker (no-tls1_3)	5m 10s
run-checker (enable-trace enable-fips)	5m 55s
run-checker (no-ui)	5m 21s
run-checker (no-quic)	5m 1s
	1h 47m 47s

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