file overwrite without checking back (.png)

[schnollk]

First of all thanks for everyones engagement for this actually simple and helpful scan tool!

One annoying thing I found, though, is when I had saved a few scans as single .png files (from within one scan session, resulting in files "Picture-1.png" to "Picture-15.png") and wanted to save some more from the second scan session. I used the same base file name ("Picture.png") and figured Simple Scan would either ask if I wanted to overwrite or start saving at "Picture-$(last digit in folder + 1).png". Simple Scan did neither. Instead I ended up with all previously saved files overwritten.

I hope I didn't miss any option settings that led to this. Other that that I think it's a bug and should at least ask the user before overwriting files.