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 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