avcodec/snow: Fix off by 1 error in run_buffer

Fixes: out of array access
Fixes: 70741/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SNOW_fuzzer-5703668010647552

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 06f5ed40f8)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/snow.c

@@ -427,7 +427,7 @@ av_cold int ff_snow_common_init(AVCodecContext *avctx){
         !FF_ALLOCZ_TYPED_ARRAY(s->spatial_dwt_buffer,  width * height) ||  //FIXME this does not belong here
         !FF_ALLOCZ_TYPED_ARRAY(s->temp_dwt_buffer,     width)          ||
         !FF_ALLOCZ_TYPED_ARRAY(s->temp_idwt_buffer,    width)          ||
-        !FF_ALLOCZ_TYPED_ARRAY(s->run_buffer, ((width + 1) >> 1) * ((height + 1) >> 1)))
+        !FF_ALLOCZ_TYPED_ARRAY(s->run_buffer, ((width + 1) >> 1) * ((height + 1) >> 1) + 1))
         return AVERROR(ENOMEM);
 
     for(i=0; i<MAX_REF_FRAMES; i++) {