Showing unstaged JSON causes: out of range integral type conversion attempted

[ignatenkobrain]

Describe the bug

Error: out of range integral type conversion attempted

To Reproduce
Steps to reproduce the behavior:

1. Open gitui with unstaged json (possibly big enough, I have https://src.fedoraproject.org/extras/pagure_owner_alias.json)
2. Click on "→" arrow

Expected behavior
gitui should not exit with an error, the json should be shown :)

Desktop (please complete the following information):

• OS: Fedora
• Version: 33

[ignatenkobrain]

Just realized that you don't have to open a diff, once you go through unstaged files and hit this json, gitui closes with an error.

[extrawurst]

@ignatenkobrain thanks for the report. I fixed the error first but I am still not happy since performance suffers when diffing giant files

[extrawurst]

Now that should do. will release a patch version later today