Is the argument "1) If not P, then not Q 2) Q 3) Therefore P" fallacious?

Hello! I encountered the following argument in the wild:

1. If God does not exist, then libertarian freedom does not exist.

2. Libertarian freedom does exist.

3. Therefore, God exists.

The closest I can come to this is the fallacy of affirming the consequent, but I don't think it is right for this argument. I give examples below that I hope demonstrate my level of understanding or my hopeless confusion! 

Fallacy of affirming the consequent:

1. If I live in Houston, then I live in California

2. I live in California

3. Therefore I live in Houston 

Below, I try to give this argument the same structure as the God argument, to see if that fixes it. I just don't see that it does:

1. If I don't live in Houston, then I don't live in California

2. I live in California

3. Therefore I live in Houston

But in the Houston example, I'm struggling to identify whether the first premise is simply not sound, or whether the structure is also not valid. Perhaps my problem with the God argument that I'm asking about is that I just don't think the first premise is sound?

Thanks!