Do not ask passphrases when a passphrase was already specified with
--passphrase option.
Add tests for --passphrase option.
Correct detecting iconv liberary with Clang.
Remove unneeded null check.
Fix the potential of a dereference of null pointer.
Remove unneeded code.
Remove unneeded length check to avoid the potential of a dereference of
null pointer.
Fix the potential of memory leaks in our test suit.
Fix the potential of memory leaks in our test suit, which
Xcode Analyzer pointed out.
Avoid code analyzer error.