Cannot open files with wrong extension

[JulianGro]

 * Xviewer version 2.4.3
 * Distribution - Linux Mint 19.3 Cinnamon

Issue Xviewer is unable to open files that have a wrong file extension. for example, when a JPEG file has a .png file extension, it will just show the error "Not a PNG file" rather than just opening it.

Steps to reproduce

• take a jpeg file
• change the file extension to png
• Xviewer will not open it anymore

Expected behaviour Xviewer should see that it is a JPEG file and should just open it.

Other information While the file extension should never be wrong, I have encountered a lot of JPEG files named PNG. I assume this might be people changing the file extension when saving a file and their application saving it as a different file type anyways.

[svastian99]

The same thing happens to me ... webp files named jpg.

[programmer-ceds]

Following the merging of PR #123 this issue can be closed now.