pictordec: decode 8bpp images when extra header marker is missing

Fixes ticket #696.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/pictordec.c

@@ -130,7 +130,7 @@ static int decode_frame(AVCodecContext *avctx,
         return AVERROR_INVALIDDATA;
     }
 
-    if (*buf == 0xFF) {
+    if (*buf == 0xFF || bpp == 8) {
         buf += 2;
         etype  = bytestream_get_le16(&buf);
         esize  = bytestream_get_le16(&buf);