ffv1: Assume bitdepth 0 means 8bit

CC: libav-stable@libav.org
Reported-by: debian/726189
(cherry picked from commit a90905db2e)
Signed-off-by: Reinhard Tartler <siretart@tauware.de>

libavcodec/ffv1dec.c

@@ -670,6 +670,7 @@ static int read_header(FFV1Context *f)
             return AVERROR(ENOSYS);
         }
         switch (f->avctx->bits_per_raw_sample) {
+        case 0:
         case 8:
             f->avctx->pix_fmt = AV_PIX_FMT_RGB32;
             break;