What does "if nothing else" mean?

I understand the meaning of "if nothing else" in sentence A, but couldn't understand the meaning in sentence B.

A. "I will go to library this afternoon if nothing else to do."

B. "Google argues that e-mail recipients have the right to view e-mail messages using the service of their choosing and that on the Internet senders are not required to consent to automated scanning, which every e-mail provider does, for security purposes if nothing else."

This usage of "if nothing else" is idiomatic, as D_Bye pointed out. In your example "... automated scanning, which every e-mail provider does, for security purposes if nothing else.", you could replace it with "if for no other purpose". It means that e-mail providers feel that security purposes are enough reason for scanning e-mails: they would scan e-mails for that reason alone anyway, so it doesn't really matter whether scanning could be justified based on other reasons.

A: Should I take some money from the company's cash box? Any reason not to?

B: Huh? What!? You might consider the possibility of getting caught, if nothing else [ = if you will consider nothing else].

B means that if A won't consider other reasons, such as the moral obligation not to steal, at least she should consider that she may get caught.

In sentence B, you can take "if nothing else" as meaning "if for no other reason".

With the example you have given therefore, Google writes that which is ultimately used for security purposes, is only for security purposes. However, it makes way for the possibility that it is also used for something else. What that might be, I'm afraid I don't know!