Unhandled git error when a tracked upstream branch is removed

[c5f]

git checkout -b some-feature
git push -u some-remote some-feature
git push some-remote :some-feature

yields the following output whenever git-radar is called on the branch with the missing upstream:

fatal: ambiguous argument 'some-remote/some-feature...HEAD': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'
Fatal: ambiguous argument 'some-remote/some-feature...HEAD': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'

The example is a silly chain of three commands to elicit this behavior, but I don't think having tracked branches deleted from remotes is an uncommon occurrence.

[hallzy]

See #86. The error looks similar and can probably be resolved with the same 2>/dev/null appending as specified there. Looks like @michaeldfallen is adding it.

[michaeldfallen]

I'm thinking squash the error as you have and create a "not upstream" indicator. Taking functionality away from the "remote commits" indicator (which honestly shouldn't be doing that not upstream functionality if we were being pure) and combines it with a "ok my upstream is configured but does it actually exist?" check.