Won't open databases with ONLY a keyfile as entry.

[subdavis]

Keyfile + password and password only confirmed working.

[subdavis]

This issue is particularly problematic when we don't know whether the user has turned password off, or simply used the empty string, which has a valid hash.

Should we support the empty string password?

I'd like to support:

• empty string + keyfile
• null + keyfile
• password no keyfile
• password and keyfile

I don't care about

• empty string + no keyfile
• null + no keyfile.

[subdavis]

This has changed in dddb196

Now, keyfile + empty string is unsupported. Which is fine with me. I can't think of a sane reason someone would have that set up.