catch all to cover when we try to view an img/video and the dir contents is empty, so nothing to show

internal/js/view_support.js

@@ -156,6 +156,8 @@ function FaceToggle()
 // also deals with fullsecreen if needed
 function ViewImageOrVideo()
 {
+    // can happen if no content to display
+    if( ! document.viewing ) return
     if( document.viewing.type.name == 'Image' )
     {
         im.src='../' + document.viewing.FullPathOnFS