avformat/nutenc: Do not pass NULL to memcmp() in get_needed_flags()

This compared to the other suggestions is cleaner and easier to understand
keeping the condition in the if() simple.

This affects alot of fate tests.

See: [FFmpeg-devel] [PATCH 05/11] avformat/nutenc: Don't pass NULL to memcmp
See: [FFmpeg-devel] [PATCH]lavf/nutenc: Do not call memcmp() with NULL argument

Fixes: Ticket 7980

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/nutenc.c

@@ -792,11 +792,12 @@ static int get_needed_flags(NUTContext *nut, StreamContext *nus, FrameCode *fc,
         flags |= FLAG_CHECKSUM;
     if (FFABS(pkt->pts - nus->last_pts) > nus->max_pts_distance)
         flags |= FLAG_CHECKSUM;
-    if (pkt->size < nut->header_len[fc->header_idx] ||
-        (pkt->size > 4096 && fc->header_idx)        ||
-        memcmp(pkt->data, nut->header[fc->header_idx],
-               nut->header_len[fc->header_idx]))
-        flags |= FLAG_HEADER_IDX;
+    if (fc->header_idx)
+        if (pkt->size < nut->header_len[fc->header_idx] ||
+            pkt->size > 4096                            ||
+            memcmp(pkt->data, nut->header    [fc->header_idx],
+                              nut->header_len[fc->header_idx]))
+            flags |= FLAG_HEADER_IDX;
 
     return flags | (fc->flags & FLAG_CODED);
 }