Bug 480536

SUMMARY
If I am working on a large project for a long time (FullHD, 886 clips), but do not close kdenlive and the computer is only switched off using hibernate (suspend to disk), then it is difficult to notice, if a used image is renamed in the file system.
This applies in particular when images, videos, titles, sounds, music, subtitles are distributed in folders in the project content. 
A renamed image is still displayed in the timeline. I assume in such a case the proxy object is displayed.
It is only informed of missing objects when kdenlive loads the project.
(Importing a project with 886 clips takes 2 minutes on my PC, AMD Ryzen 5 3600, 32GB Ram, Disk: SSD)
In the rendered video, the image was displayed as INVALIDE, but you only notice this when the movie is viewed. 
Rendering of the 1:45 hour long project takes 1.5 hours 1920x1080, NVENC H264 ABR.

If such a check would take a long time, then it could be switched on/off in the project settings.

STEPS TO REPRODUCE
1. Create a longer project using movies and images which will need proxy clips. Do NOT restart kdenlive during edit the project.
2. Rename a image in the filesystem which are used in the timeline
3. render the project

OBSERVED RESULT
No info from kdenlive about the missing image. Instead of the (missing) image the text "INVALIDE" is displayed in the movie.

EXPECTED RESULT
Before start to render a project kdenlive should inform the user that objects are missing.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: openSUSE Leap 15.5
(available in About System)
kdenlive: kdenlive-23.08.4-x86_64-A.AppImage
KDE Plasma Version: 
KDE Frameworks Version: 5.112.0
Qt Version: 5.15.10
MLT: 7.21.0 

ADDITIONAL INFORMATION