ClientHandle::insert() should not consume a block when it fails

[gsnoff]

Currently, the insert() method of ClientHandle accepts a Block instance only by value, forcing its consumption, regardless of whether the insert operation runs successfully or not. This introduces unnecessary hassle with contents cloning (and keeping in RAM), whenever implementing repeating attempts of inserting the data.

Ideally, the Block should be taken by reference instead. Failing that, it should be returned back in the Result error value.

[suharev7]

Thanks for the advice. The implementation of this has already been pushed into this repository and will be in the next release.