Fix image loading performance
Summary: Start the dirlister after loading an image whose url is passed on the command line to make sure that this image is shown before the possibly long running dirlister on a potentially slow device is started.
Mount some slow network filesystem (e.g. cifs) and open an image file
from a directory containing a few hundred files using the command line:
$ gwenview imagefile
It will take several seconds/minutes until the image is shown (until all
preview images are loaded).
After applying this patch the image will be shown immediately and the
preview images after that.
Reviewers: Gwenview, ngraham
Reviewed By: Gwenview, ngraham
Subscribers: ngraham, tommo
Differential Revision: https://phabricator.kde.org/D25005