Bug in `git branch --delete main` when on other orphan branch

[Martin von Zweigbergk <martinvonz@xxxxxxxxxx>]

Hi,

I did this:
git init test
cd test
echo a > file
git add file
git commit -m a
git checkout --orphan other
git branch --delete main

The last command fails with:
fatal: Couldn't look up commit object for HEAD

That's a bug, right? I can of course work around it with `rm
.git/refs/heads/main`.