Remove branching in read_config_to_string

[Masynchin]

I have deleted this if-let branching, so that function becomes oneliner. I would use flat_map with closure, but it seems it is not welcomed here :)

I didn't test this changes, so I expect to be supervised by CI.

[solidiquis]

Thanks for the contribution @Masynchin :]

If you wouldn't mind taking care of the merge conflict I'd be happy to merge this in.

[Masynchin]

Haven't resolve merge git conflicts for a while, but here we go. Did I do it right? Hope it is all right.

[solidiquis]

Yes you did :]

Thanks for the contribution!