h264: Use mismatching frame numbers in fields to synchronize the

first/second field state independant of them being reference or not.
Fixes Ticket354

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/h264.c

@@ -2946,11 +2946,9 @@ static int decode_slice_header(H264Context *h, H264Context *h0){
                 s0->first_field = FIELD_PICTURE;
 
             } else {
-                if (h->nal_ref_idc &&
-                        s0->current_picture_ptr->f.reference &&
-                        s0->current_picture_ptr->frame_num != h->frame_num) {
+                if (s0->current_picture_ptr->frame_num != h->frame_num) {
                     /*
-                     * This and previous field were reference, but had
+                     * This and previous field had
                      * different frame_nums. Consider this field first in
                      * pair. Throw away previous field except for reference
                      * purposes.