Splat when GHToggleThreads is run against a hunk with no thread / comments

[joestringer]

I tried to use GHToggleThreads on a hunk I was viewing, without realizing that there are no existing comments / threads. Here's the splat:

Error executing Lua callback: /home/joe/.vim/bundle/gh.nvim/lua/litee/gh/pr/diff_view.lua:526: attempt to index field 'threads_by_line' (a nil value)                                                                                                                                       
stack traceback:                                                                                                                                                                                                                                                                            
        /home/joe/.vim/bundle/gh.nvim/lua/litee/gh/pr/diff_view.lua:526: in function 'toggle_threads'                                                                                                                                                                                       
        /home/joe/.vim/bundle/gh.nvim/lua/litee/gh/commands.lua:45: in function </home/joe/.vim/bundle/gh.nvim/lua/litee/gh/commands.lua:45> 

[ldelossa]

Wow, I can't believe I haven't seen that one before. Should be an easy fix. I'll ping this with the commit.

[ldelossa]

Fixed @joestringer