dolphinview: Update thumbnail on filename change

If filename of an item was updated previously, it would modify the model before the file was actually changed. This led to the model calling a signal that would try to run a previewjob, but since the filename is not actually changed yet on disk, it would fail.

This patch moves the model updating after copyjob. Copyjob will take care of the file renaming if there is already existing file. We just need to update the model correctly after the job has succeeded.

(cherry picked from commit eca160ae)