Abort doesn't restore the branch position

As of today, it happens with bug 15516

git bz apply 15516
[....]
Applying: Bug 15516: Add ability to create hold groups from OPAC
error: sha1 information is lacking or useless (koha-tmpl/opac-tmpl/bootstrap/en/modules/opac-reserve.tt).
error: could not build fake ancestor
Patch failed at 0001 Bug 15516: Add ability to create hold groups from OPAC
hint: Use 'git am --show-current-patch=diff' to see the failed patch
When you have resolved this problem run "git bz apply --continue".
If you would prefer to skip this patch, instead run "git bz apply --skip".
To restore the original branch and stop patching run "git bz apply --abort".
Patch left in /tmp/Bug-15516-Add-ability-to-create-hold-groups-from-O-YaW1QE.patch

# see the commit where the apply is stuck
git log --oneline
2fdfa85217 (HEAD -> testing-SO-QA) Bug 15516: Fix hold groups for multi items for one bib

git bz apply --abort
# no output

# still at the same commit, git status is clean
git log --oneline
2fdfa85217 (HEAD -> testing-SO-QA) Bug 15516: Fix hold groups for multi items for one bib

version of git bz: 8fd0053f it's the current apply_on_cascade branch of repo gitlab.com:koha-community/git-bz