Improve error message for tumbler file size config option

Submitted by trz..@..as.com

Assigned to Ali Abdallah @ali

Link to original bug (#16600)

Description

Today, I decided to try and fix that thunar (and tumbler) wouldn't display any thumbnails for movies I had on my harddrive but would generate them for everything else. Long story short, I spent way too much time figuring out that everything was working as expected, and the thumbnail generator plugins wouldn't be called because the file size limit was set to a value too low. When monitoring with busctl though, it just showed me that it couldn't find any handlers for that particular file among the configured ones.

My proposal would be to add an extra message that tells the user "I have a handler for this case, but I cant use it because of the FileSizeLimit setting for it", as that would be way less confusing than the current message for users who might have the same problem as myself. I understand that adding an error for every possible config setting might be very confusing, but currently there is only one that might block a plugin from being used, the FileSizeLimit.