Autosaves: protect against rare failures that may occur mid-loading

Hard to know what might cause a failure during the load function of a
verified Autosave, but it's not impossible that someone could do
something dumb like unmount the device with the autosave files while the
load is occurring.  In this case, the function will now fail gracefully
instead of bringing down the whole program.
Effects > Artistic > Stained Glass: wrap up initial build

Dialogs like this demonstrate the need for separating "basic" and
"advanced" settings for certain tools.  One or two key sliders should be
made available on most effects, while others could be hidden behind a
second tab (or my personal preference, a tab-like button bar a la iOS:
http://cdn1.appleinsider.com/safari-130620-3.png).  A user control like
this is on my to-do list, with about a million other UI items.

In the meantime, this tool was a nice distraction from my usual tedious
pre-release work.  Not only is it very fast, but it's a unique filter
not found in any free photo editors (to my knowledge), and a totally
different, much more elegant piece of work than Photoshop's lame Texture
> Stained Glass feature.  Also, I got a very nice Voronoi class out of
it, which could prove useful in the future - a 2 for 1 effort, yay!