Network Filesharing: Fix compile warnings and trivial improvements

Summary:
Fix compile warnings:
warning: zero as null pointer constant
warning: variable ‘result’ set but not used

Additionally some improved overloads and formatting which does not
deserve a sepearte patch ;-).

Test Plan: Compiles

Reviewers: Dolphin, ngraham, mlaurent

Reviewed By: Dolphin, ngraham

Differential Revision: https://phabricator.kde.org/D29105