Image files detection does not work properly

[LMH01]

Describe the bug
See #127 :

I just tested it and I can't quite replicate the problem:

Everything works flawlessly when I do the following:

1. Create new Initial backup
2. Start Mod-Tool and import the extracted .zip file
3. Check box that allows modification of already existing content
4. Import works without problems
5. Check if the png files are missing, they are still there

Oddly what did not work properly was importing the .zip file. When I imported the .zip file (so that the tool needed to extract the files) some problems occurred, mainly that some image files are missing. So it seems like something either with the .zip file is broken or that the extraction method is broken somehow. This will have to be tested separately. I will create a new issue for that.

Edit: Maybe this is also somehow related to the operating system. I performed my tests under Linux.

To Reproduce
Steps to reproduce the behavior:
Do the same as above accept that the .zip file is selected.

Expected behavior
The image files should not be missing

Screenshots

Desktop (please complete the following information):

• OS: Linux, Windows
• Version v4.9.0-beta4

Additional context

[LMH01]

The zip file extraction was not the problem, the problem was a false heuristic for the detection of platform image files.