[4/4] windowscodecs: Add stub IWICMetadataBlockReader to PNG decoder.

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
http://testbot.winehq.org/JobDetails.pl?Key=18675

Your paranoid android.


=== WXPPROSP3 (32 bit metadata) ===
metadata: unhandled exception c0000005 at 4CCA826D

=== W2K8SE (32 bit metadata) ===
metadata: unhandled exception c0000005 at 72C28045