After editing an image (e.g. rotate) a new thumbnail is created but
it is not repainted in the View Mode thumbnail bar.
The custom signals documentChanged and busyStateChanged provide
a QModelIndex for the modified document but this is based on the
source model and cannot be used in ThumbnailBarView where the list
view is based on a filtered proxy model and the index is wrong or
does not exist in some cases.
This patch uses the QUrl as argument for both signals and gets the
proper index for the current model in the receiver view.