libavcodec/mpegvideo.c:2321: error: Null Dereference
  pointer `desc` last assigned on line 2320 could be null and is dereferenced at line 2321, column 18.

libavcodec/mpegvideo.c:2315:1: start of procedure ff_draw_horiz_band()
2313.  * @param h is the normal height, this will be reduced automatically if needed for the last row
2314.  */
2315. void ff_draw_horiz_band(AVCodecContext *avctx, DSPContext *dsp, Picture *cur,
      ^
2316.                         Picture *last, int y, int h, int picture_structure,
2317.                         int first_field, int low_delay,

libavcodec/mpegvideo.c:2320:5: 
2318.                         int v_edge_pos, int h_edge_pos)
2319. {
2320.     const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(avctx->pix_fmt);
          ^
2321.     int vshift = desc->log2_chroma_h;
2322.     const int field_pic = picture_structure != PICT_FRAME;

libavutil/pixdesc.c:1507:1: start of procedure av_pix_fmt_desc_get()
  1505. }
  1506. 
  1507. const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
        ^
  1508. {
  1509.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)

libavutil/pixdesc.c:1509:9: Taking false branch
  1507. const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
  1508. {
  1509.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)
                ^
  1510.         return NULL;
  1511.     return &av_pix_fmt_descriptors[pix_fmt];

libavutil/pixdesc.c:1509:24: Taking true branch
  1507. const AVPixFmtDescriptor *av_pix_fmt_desc_get(enum AVPixelFormat pix_fmt)
  1508. {
  1509.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)
                               ^
  1510.         return NULL;
  1511.     return &av_pix_fmt_descriptors[pix_fmt];

libavutil/pixdesc.c:1510:9: 
  1508. {
  1509.     if (pix_fmt < 0 || pix_fmt >= AV_PIX_FMT_NB)
  1510.         return NULL;
                ^
  1511.     return &av_pix_fmt_descriptors[pix_fmt];
  1512. }

libavutil/pixdesc.c:1512:1: return from a call to av_pix_fmt_desc_get
  1510.         return NULL;
  1511.     return &av_pix_fmt_descriptors[pix_fmt];
  1512. }
        ^
  1513. 
  1514. const AVPixFmtDescriptor *av_pix_fmt_desc_next(const AVPixFmtDescriptor *prev)

libavcodec/mpegvideo.c:2321:5: 
2319. {
2320.     const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(avctx->pix_fmt);
2321.     int vshift = desc->log2_chroma_h;
          ^
2322.     const int field_pic = picture_structure != PICT_FRAME;
2323.     if(field_pic){
