Added missing image format
Summary:
QImage::Format_ARGB6666_Premultiplied was missing from the image format table.
This might have caused some bugs later on.
See: http://doc.qt.io/qt-5/qimage.html#Format-enum
Reviewers: fredrik, KWin
Reviewed By: fredrik
Subscribers: cfeck, kwin, KWin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D10497