Updated folder preview base template

mod/filesystem/metadata/folder.go

@@ -27,6 +27,10 @@ func generateThumbnailForFolder(cacheFolder string, file string, generateOnly bo
 	}
 
 	//Load the base template
+	if !fileExists("web/img/system/folder-preview.png") {
+		//Missing system files. Skip rendering
+		return "", errors.New("Missing system template image file")
+	}
 	image1, err := os.Open("web/img/system/folder-preview.png")
 	if err != nil {
 		return "", err