indeo5: reject negative motion vectors

Reported-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org

libavcodec/indeo5.c

@@ -520,6 +520,12 @@ static int decode_mb_info(IVI45DecContext *ctx, IVIBandDesc *band,
                         mv_x += IVI_TOSIGNED(mv_delta);
                         mb->mv_x = mv_x;
                         mb->mv_y = mv_y;
+                        if (mv_x < 0 || mv_y < 0) {
+                            av_log(avctx, AV_LOG_ERROR, "Invalid MV %d %d\n",
+                                   mv_x, mv_y);
+                            mb->mv_x = mb->mv_y = 0;
+                            return AVERROR_INVALIDDATA;
+                        }
                     }
                 }
             }