Closing the bitmapstream for UnknownBitMapDecoder (#8174)

* close the bitmapstream

* move closing stream to catch

Author: singhashish-wpf

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Imaging/BitmapDecoder.cs

@@ -1190,6 +1190,7 @@ out decoder
             }
             catch
             {
+                bitmapStream.Close();
                 #pragma warning disable 6500
 
                 decoderHandle = null;