totp issuer can be optional

[nxm]

Hello,

it seems that issuer can be optional in totp

• https://github.com/google/google-authenticator/wiki/Key-Uri-Format#issuer
• https://docs.yubico.com/yesdk/users-manual/application-oath/uri-string-format.html#label
• https://www.ietf.org/id/draft-linuxgemini-otpauth-uri-01.html#name-issuer-parameter-optional

[tommie]

I agree with your reading of the specs.

What is the point of making it a pointer, rather than just treating the empty string as missing? Is there any time the empty-string issuer would make sense?

[yogo1212]

good find!

could you separate the whitespace fixes from the feature? (in a second commit)

i also agree that using the empty string might be the better idea but i don't really mind.