"attempt to perform arithmetic on field 'right_offset'" when opening PR

[proivk]

Issue Description

Error appears when opening some PRs

Describe what you expected to happen

No error appears when opening PR

How to reproduce it (as minimally and precisely as possible)

*currently it reproduces on my private repository so I can't share exact PR with you where this issue appears.

1. Octo pr list
2. Select PR from the list and hit Enter

Type: bug report

Describe what happened (or what feature you want)

Error appears

error executing vim.schedule lua callback: ...m/site/pack/packer/opt/octo.nvim/lua/octo/ui/writers.lua:688: attempt to perform arithmetic on field 'right_offset' (a nil value)
stack traceback:
        ...m/site/pack/packer/opt/octo.nvim/lua/octo/ui/writers.lua:688: in function 'write_thread_snippet'
        ...m/site/pack/packer/opt/octo.nvim/lua/octo/ui/writers.lua:1318: in function 'write_threads'
        ...pack/packer/opt/octo.nvim/lua/octo/model/octo-buffer.lua:179: in function 'render_issue'
        ...re/nvim/site/pack/packer/opt/octo.nvim/lua/octo/init.lua:253: in function 'create_buffer'
        ...re/nvim/site/pack/packer/opt/octo.nvim/lua/octo/init.lua:82: in function 'cb'
        ...re/nvim/site/pack/packer/opt/octo.nvim/lua/octo/init.lua:107: in function 'cb'
        ...nvim/site/pack/packer/opt/octo.nvim/lua/octo/gh/init.lua:106: in function ''
        vim/_editor.lua: in function <vim/_editor.lua:0>

After that PR opens as usual

Tell us your environment

NVIM v0.8.3 Octo -> latest MacOs -> latest iTerm2

Anything else we need to know?