index template will output commit-id line only if available

tpl/index

@@ -84,7 +84,9 @@ cat <<EOF
       )
       <div>Copyright &copy; $yearrange $copyright</div>
       <div>Last Updated: $( ./tsdate "$lastts" '%F %H:%M:%S' )</div>
-      <div class="commit-id">$lasthash</div>
+      $( [ -n "$commit-id" ] \
+        && printf '<div class="commit-id">%s</div>' "$lasthash"
+      )
     </footer>
   </body>
 </html>