Before this patch, when you forced Krita to load file in
unknown format, it showed uncancelled progress bar and
showed the file in Recent Documents.
It happened when you dragged and dropped file to the
welcome screen or import animation frames or use Open->File
or Open -> Recent Files.
Progress bars were visible only when some image was opened.
This commit cancels progress bars and make sure unloadable
files are not added to Recent Documents.