Empty window in GitUp port

[Ethan C]

Hi everyone,

       I have encountered a rather hairy issue, which I believe most 
likely lies in gnustep-gui but in fact could lie anywhere in the dozens 
of dependencies my project has. I am currently porting the macOS Git 
client GitUp <https://github.com/git-up/GitUp> to GNUstep on Clang on 
Linux, and the examples for using the underlying Git library called 
GitUpKit are failing to work properly. The example GitDiff launches and 
allows you to select a repository to view. However, it immediately 
closes. When I modify -[AppDelegate 
applicationShouldTerminateAfterLastWindowClosed:] to return NO, then it 
displays an empty window. The same happens with GitDown. Meanwhile, the 
example GitY uses a hacky way to allow selecting repositories with the 
file picker (which I think is unnecessary), and due to its hacky nature 
it doesn't work on GNUstep. I might look into that more, but the issue 
of the empty window is very perplexing. I have a build guide available 
at 
https://github.com/ethanc8/GitUp/blob/gnustep/GitUpKit/DebianBuildGuide.md, 
and a more detailed explanation of the issue at 
https://github.com/ethanc8/GitUp/issues/1.

Thanks,

Ethan