externalDiffCommand doesn't work when diffing between 2 refs

[l0ngvh]

Is your feature request related to a problem? Please describe.
externalDiffCommand currently works wonder when viewing the diff of each commits, but it doesn't work when we're diffing between 2 refs (with W key binding). Instead Lazygit used the default diff view

Describe the solution you'd like
externalDiffCommand should also applies to diff view between to refs.

Describe alternatives you've considered
The default diff view is good enough, but I prefer to use difftastic to view the diff.

Additional context

Normal diff:

Diff between branches:

I could help with implementing this, but I don't know where to start. Any help would be appreciated.

[stefanhaller]

Should be fixed by #3519, could you test this?

[l0ngvh]

@stefanhaller Thanks for the swift response. Can confirm it working as expected now