* fixing an unitilaized field AVImageInfo::interleaved.

      As a matter of fact we have two problems here: first
      AVImageInfo::interleaved is never initialzed in img.c.
      The second problem is that even if we want interleaved
      PNGs there's a bug in png.c that prevents us from generating
      them.

      The later problem is for somebody familiar with PNG to
      handle.

      And yes, always setting AVImageInfo::interleaved to 0 isn't
      such a good idea, but it still beats garbage values.
orginal commit by roman shaposhnik

Originally committed as revision 2380 to svn://svn.ffmpeg.org/ffmpeg/trunk