fix: get invalid ASDF_DATA_DIR when exec asdf shims by non-shell (#1154)

* fix: get invalid ASDF_DATA_DIR when exec asdf shims by non-shell

asdf_data_dir function inits ASDF_DATA_DIR with HOME when value is empty.
HOME may replace to empty string when asdf shims called by non-shell program.
this makes invalid value of ASDF_DATA_DIR.

lib/utils.bash

@@ -41,8 +41,10 @@ asdf_data_dir() {
 
   if [ -n "${ASDF_DATA_DIR}" ]; then
     data_dir="${ASDF_DATA_DIR}"
-  else
+  elif [ -n "$HOME" ]; then
     data_dir="$HOME/.asdf"
+  else
+    data_dir=$(asdf_dir)
   fi
 
   printf "%s\\n" "$data_dir"