Do not return stuff on unserialize

Fixes #14.

I did some regex searches in our code base and could not find a place where `unserialize` is called and expected to have a return value (I tried to search for stuff like `... = ...->unserialize( ... )` as well as `...( ..., ...->unserialize( ... ) ... )`).

This is obviously not urgent at all. Please double-check.