D26103: Put Q_REQUIRED_RESULT in front of the functions to fix builds with [[nodiscard]]

[Hannah von Reth]

vonreth added a reviewer: sitter.

REPOSITORY
  R241 KIO

REVISION DETAIL
  https://phabricator.kde.org/D26103

To: vonreth, sitter
Cc: kde-frameworks-devel, LeGast00n, GB_2, michaelh, ngraham, bruns