Setting prefix to "." saves screenshots as hidden files without user warning

Bug Description

In Kazam's preferences, users can set the "Filename prefix" field to any string. When the user sets this prefix to . (dot) and takes a screenshot, Kazam successfully generates the screenshot file. However, because files beginning with a dot are treated as hidden files on Linux systems, the generated file is not visible in the default file manager or with the ls command. The application provides no warning or indication to the user that this prefix will result in a hidden file, leading users to mistakenly believe the screenshot was lost or failed to save.

Steps to Reproduce
1.Open Kazam
2.Go to Preferences → Screencast/Screenshot
3.Set the "Filename prefix" field to .
4.Close the preferences window
5.Take a screenshot
6.Open the file manager or use ls command to check the save directory

Environment
Kazam version:1.4.5、2.0.0
OS: Ubuntu 22.04