Refactor encrypted_add_password(). #3901

Job	Run time
cmake-offline-googletest	4m 44s
cmake-offline-googletest-src	4m 52s
system-sexpp, sexpp shared libs on, rnp shared libs on	2m 52s
package-source	36s
system-sexpp, sexpp shared libs on, rnp shared libs off	3m 0s
ubuntu-latest [CC gcc; botan; shared libs on; GnuPG stable]	4m 23s
system-sexpp, sexpp shared libs off, rnp shared libs on	2m 50s
ubuntu-latest [CC clang; botan; shared libs on; GnuPG stable]	4m 39s
system-sexpp, sexpp shared libs off, rnp shared libs off	2m 49s
ubuntu-latest [CC gcc; openssl; shared libs on; GnuPG stable]	5m 23s
ubuntu-latest [CC clang; openssl; shared libs on; GnuPG stable]	4m 23s
ubuntu-20.04 [CC gcc; openssl; shared libs on; GnuPG stable]	3m 55s
ubuntu-latest [CC gcc; botan; shared libs off; GnuPG stable]	4m 24s
package	1m 0s
debian-tests	18s
	50m 8s

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