Previously, GwenviewConfig::jPEGQuality() was being used only by
updateRawDataFromImage() in jpegcontent.cpp. updateRawDataFromImage() is called
only when d->mImage is not null, implying that only "modified" jpeg
images get written to disk with the user's set quality level. This patch
unconditionally saves jpeg images to disk at the set quality level.

Also, this patch fixes a race condition introduced by merge request !26


We now wait for the save KJob to finish before restoring the quality
level.

Signed-off-by: Madhav Kanbur <abcdjdj@gmail.com>