avfilter/vf_pullup: do not ignore frame field order

Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavfilter/vf_pullup.c

@@ -657,7 +657,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
                   (const uint8_t**)in->data, in->linesize,
                   inlink->format, inlink->w, inlink->h);
 
-    p = !!in->interlaced_frame;
+    p = in->interlaced_frame ? !in->top_field_first : 0;
     pullup_submit_field(s, b, p  );
     pullup_submit_field(s, b, p^1);