title: PdfSharp Image Filter is empty string
body: <p>I have a pdf I'm trying to decode.
  For the first several pages of the document the image type is &quot;/FlateDecode&quot;.
  Suddenly the image type becomes am empty string (&quot;&quot;) for the rest of the document.
  The rest of the fields appear to be Ok. (Height,Width, etc).
  Does this mean I should use the previous valid decode type?</p>