fix decoding of the first frame of gray.mov

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@11169 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/mjpegbdec.c

@@ -109,7 +109,7 @@ read_header:
     if (s->interlaced) {
         s->bottom_field ^= 1;
         /* if not bottom field, do not output image yet */
-        if (s->bottom_field && second_field_offs)
+        if (s->bottom_field != s->interlace_polarity && second_field_offs)
         {
             buf_ptr = buf + second_field_offs;
             second_field_offs = 0;