fix: when loading ignores files that are not text files.

[AlexBCa]

This contribution fixes issue #1323.

In this small change, an exception is handled if the file cannot be opened because it is not a text file; it simply ignores it and loads the project.

This is my first contribution to the project, and I wanted to do something simple, although I have ideas for refactoring the project loading to make it more robust. If you are open to some refactoring, I would appreciate any feedback so I can get started, knowing what is currently being sought in the project.

[TheJackiMonster]

Sounds good to me. Theoretically I've already started on a separate branch to make bigger changes to the IO code. You can find it here:

• https://github.com/olivierkes/manuskript/tree/gtk/manuskript/io
• https://github.com/olivierkes/manuskript/tree/gtk/manuskript/data

Also I think most details about the changes I made so far can be read in issue #1117. So feel free to look into it and change or improve it. I'd also be happy to see someone try porting equivalent changes into the Qt code base since my changes only work on the GTK port/branch. But either way making the IO code more reliable is great.