D15074: [server] Do not try to create data offers without source

[Eike Hein]

hein accepted this revision.
This revision is now accepted and ready to land.

REPOSITORY
  R127 KWayland

BRANCH
  offerWithSourceOnly

REVISION DETAIL
  https://phabricator.kde.org/D15074

To: romangg, #kwin, hein
Cc: kde-frameworks-devel, michaelh, ngraham, bruns