DocumentViewer: Fix freefile when loading file as stream

Controls.DocumentViewer/DocumentViewer.vb

@@ -127,7 +127,7 @@ Public Class DocumentViewer
     End Sub
     Private Sub FreeFile()
         Try
-            If Len(_FilePath) Then
+            If Len(_FilePath) OrElse _Fileinfo Is Nothing Then
                 Exit Sub
             End If
             Dim oExtension As String = _Fileinfo.Extension.ToUpper