fixed seg fault while recovering wallet by making encryption optional…

[jeredkenna]

I was getting a seg fault trying to recover a wallet and save it without a password.
Really simple change but if you want to pull this and branch it then some people might find the version useful.

[JamesANZ]

Hi, when it gives a segment fault does that mean that the passphrase is incorrect if a passphrase is provided? Thanks

[jackjack-jj]

It's actually a choice to enforce encryption of recovered wallets, I don't want to be responsible of leaked keys
I could have been clearer though so I'll leave that open until done
Also I don't get how this can lead to a segfault

[wendtl]

I ran into this issue when I was using an older version of pywallet. I did not have pycrypto properly installed and installing it correctly fixed the issue. I'd have to revisit the updated code to see if I can still replicate the issue but I believe it had something to do with the fallback that was being used when pycrypto was not installed.