Since 4a3b6bfeac, there should be a loading/wait icon while the previews
are being loaded. However when initially loading the file list, the big
document icon we use when no preview was found showed up for a short
moment. This is because preview loading is only triggered after the file
list is fully loaded, and so the preview loading tag isn't set yet. But
we only checked for this tag. Now the waiting icon is displayed when
either the file list or the preview is still loading.
d695619a55