make release fails when HEAD is detached head

[BrendanCunningham]

make release at a named head (e.g. master) succeeds:

bcunningham@cn-priv-03:rtslib-fb (master)$ git branch
* master
bcunningham@cn-priv-03:rtslib-fb (master)$ git show HEAD
commit 99a637156bd4f910a4b993e879589ddd0312a39d (HEAD -> master, origin/master, origin/HEAD)
Merge: 86ff610 66264ea
Author: Maurizio Lombardi <[email protected]>
Date:   Thu Sep 1 16:13:17 2022 +0200

    Merge pull request #186 from Kidwithservers/master

    Fix inability to create ACLs for some FC cards

bcunningham@cn-priv-03:rtslib-fb (master)$ make release
Exporting the repository files...
Cleaning up the target tree...
Fixing version string...
Generated release tarball:
    dist/rtslib-fb-2.1.75.4.g99a6371.tar.gz

But make release on a detached head fails. For example, the commands below try to do make release from the same commit as master in the above successful make release:

bcunningham@cn-priv-03:rtslib-fb (master)$ git clean -ffxd
Removing build/
Removing dist/
bcunningham@cn-priv-03:rtslib-fb (master)$ git checkout 99a637156bd4f910a4b993e879589ddd0312a39d
Note: checking out '99a637156bd4f910a4b993e879589ddd0312a39d'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by performing another checkout.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -b with the checkout command again. Example:

  git checkout -b <new-branch-name>

HEAD is now at 99a6371 Merge pull request #186 from Kidwithservers/master
bcunningham@cn-priv-03:rtslib-fb ((99a6371...))$ make release
Exporting the repository files...
fatal: Not a valid object name
tar: This does not look like a tar archive
tar: Exiting with failure status due to previous errors
make: *** [Makefile:44: build/release-stamp] Error 2