Bug: receive.denyCurrentBranch fails if core.bare unset

Hi,

When I set "receive.denyCurrentBranch" to "refuse", it still have the
behavior of ignore. On newly created repository, core.bare is always
set, but I had a old non-bare repository where it is unset. With
core.bare unset, rev-parse --is-bare-repository returns true in .git,
but false in the worktree.

What should be the right fix for this problem? Adding in the
documentation of receive.denyCurrentBranch that setting
core.bare explicitely is highly recommended ?

Br,
Alban