[ticket/16604] Display warning messages on storage path setting issues

PHPBB3-16604

phpBB/adm/style/acp_storage.html

@@ -27,6 +27,13 @@
 	</tbody>
 </table>
 
+{% if S_ERROR %}
+	<div class="errorbox">
+		<h3>{{ lang('WARNING') }}</h3>
+		<p>{{ ERROR_MSG }}</p>
+	</div>
+{% endif %}
+
 <form id="acp_storage" method="post" action="{{ U_ACTION }}">
 
 	{% for storage in STORAGES %}