Bugfix: Segfault when running paranoid config in verbose mode

[jetwhiz]

When "external IV chaining" is enabled, cipherName_ parameter may be NULL, resulting in segfault in verbose log attempt

[rfjakob]

I'm sure the patch fixes the crash, but the actual bug is that cipherName_ is null, no?

[jetwhiz]

@rfjakob -- from what I understand, it is normal for this to be possibly null for external IV chaining during a call to findOrCreate (create):

encfs/encfs/DirNode.cpp

Line 642 in b0ef1d7

if (fsConfig->config->externalIVChaining) node->setName(0, 0, iv);

[rfjakob]

I see. I think @vgough will agree that this is good to merge. Thanks!