guess media type by filename extension when mimetype is missing

js/interface_common.js

@@ -978,6 +978,11 @@ function startTorrentDownloadAndPreview(torrentId, previewContainer, isMedia) {
 }
 
 function webtorrentFilePreview(file, previewContainer, isMedia) {
+    if (!isMedia) {
+        // try guessing by filename extension
+        isMedia = /^[^?]+\.(?:jpe?g|gif|png|mp4|webm|mp3|ogg|wav|)$/i.test(file.name)
+    }
+    
     if (isMedia) {
         var imagePreview = $('<div class="image-preview" />');
         previewContainer.append(imagePreview);