Better DETACHED_HEAD detection

functions/vcs.zsh

@@ -63,7 +63,7 @@ function +vi-git-remotebranch() {
 function +vi-git-tagname() {
   # Only show the tag name if we are not in DETACHED_HEAD state,
   # since in that case it would already be displayed in the branch segment
-  if [[ -n "$(git status | grep 'HEAD detached')" ]] ; then
+  if [[ -z "$(git symbolic-ref HEAD 2>/dev/null)" ]] ; then
     local tag
 
     tag=$(git describe --tags --exact-match HEAD 2>/dev/null)