Add an option to purge "error" entries from the cache

[pierrre]

I'm using czkawka/krokiet to find similar/duplicate videos on my computer.
I've got tens of thousands of videos, and tens of TB.
Doing a scan takes days.

When krokiet (actually ffmpeg) is processing a high resolution video (usually 4k), it uses a lot of memory.
If it's configured to use a high number of threads, it may run out of memory. (I guess ffmepg crashes)
When it happens, we get a strange error message Failed to hash file, reason Too short.
Then the file is added to the cache with the error message, and is never scanned again ever.

I found a workaround in this comment #605 (comment)
I just need to reduce the number of threads.
Then, fewer ffmpeg processes are running concurrently, and there is no "out of memory" issue.

The problem: some files are still stored in the cache with the error message.
I can't scan them again with a lower number of threads.
If I want to be able to scan them, I need to delete the entire cache files.
Then it will take me again days to scan all the videos.

Could you add an option/button, to purge the "error" entries from the cache ?
Thank you 😃