Fix missing filename in header of mobile preview for plain text attachments

skins/elastic/templates/messagepart.html

@@ -14,7 +14,7 @@
 <div class="content selected">
 	<h2 id="aria-label-toolbar" class="voice"><roundcube:label name="arialabeltoolbar" /></h2>
 	<div class="header" role="toolbar" aria-labelledby="aria-label-toolbar">
-		<span class="header-title"></span>
+		<span class="header-title"><roundcube:var name="env:filename" /></span>
 		<div id="messagetoolbar" class="toolbar">
 			<a class="button properties" id="properties-button" href="#properties" onclick="UI.show_sidebar()" data-hidden="big">
 				<span class="inner"><roundcube:label name="properties"></span>