Bug 455321

SUMMARY
Hi, when I double click to preview in Gwenview my huge collection of Krita files; a minority are read without any problems, and a majority will simply don't load. They display a red box on the center of the viewport with the message "Loading 'filename.kra' failed". 

STEPS TO REPRODUCE
1.  Download this Krita file (ziped) : https://www.peppercarrot.com/0_sources/0ther/artworks/zip/2017-10-11_run_by-David-Revoy.zip
2.  Open it with Gwenview (from Dolphin or from Konsole)

OBSERVED RESULT
Gwenview display a red box on the center of the viewport with the message "Loading 'filename.kra' failed". 

Output on terminal:
```
~/peppercarrot/webcomics/0ther/artworks »»» gwenview 2017-10-11_run.kra 
   kf.i18n.kuit: "Unknown subcue ':whatsthis,' in UI marker in context {@info:whatsthis, %1 the action's text}."
   org.kde.kdegraphics.gwenview.lib: Unresolved mime type  "image/x-mng"
   org.kde.kdegraphics.gwenview.lib: Unresolved raw mime type  "image/x-nikon-nrw"
   org.kde.kdegraphics.gwenview.lib: Unresolved raw mime type  "image/x-samsung-srw"
   org.kde.kdegraphics.gwenview.lib: QImageReader::read() using format hint "kra" failed: "Unknown error"
   org.kde.kdegraphics.gwenview.lib: QImageReader::read() without format hint failed: "Unsupported image format"
   org.kde.kdegraphics.gwenview.lib: QImageReader::read() using format hint "kra" failed: "Unknown error"
   org.kde.kdegraphics.gwenview.lib: QImageReader::read() without format hint failed: "Unsupported image format"
```

EXPECTED RESULT
Gwenview loads  the Krita image.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Linux workstation 5.17.13-300.fc36.x86_64 / Plasma 
KDE Plasma Version: 5.24.5
KDE Frameworks Version: 5.93.0
Qt Version: 5.15.3