avcodec/jpeg2000dec: jpeg2000 has its own lowres option

jpeg2000 overrides the global lowres variable with a lowres field called reduction_factor
ffmpeg -lowres X causes the reduction_factor to be set
ffplay -lowres X causes both lowres and the reduction_factor to be set
ossfuss sets only lowres

only the ffmpeg variant works. This patch tries to make the other 2 work.

Alternative we could just error out if things are inconsistent.
More complex restructuring should be limited to the master branch
to keep this reasonably easy to backport

Fixes: out of array access
Fixes: 59672/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_JPEG2000

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/jpeg2000dec.c

@@ -308,7 +308,7 @@ static int get_siz(Jpeg2000DecoderContext *s)
         dimy = FFMAX(dimy, ff_jpeg2000_ceildiv(o_dimy, s->cdy[i]));
     }
 
-    ret = ff_set_dimensions(s->avctx, dimx, dimy);
+    ret = ff_set_dimensions(s->avctx, dimx << s->avctx->lowres, dimy << s->avctx->lowres);
     if (ret < 0)
         return ret;
 
@@ -2426,6 +2426,14 @@ static av_cold int jpeg2000_decode_init(AVCodecContext *avctx)
 {
     Jpeg2000DecoderContext *s = avctx->priv_data;
 
+    if (avctx->lowres)
+        av_log(avctx, AV_LOG_WARNING, "lowres is overriden by reduction_factor but set anyway\n");
+    if (!s->reduction_factor && avctx->lowres < JPEG2000_MAX_RESLEVELS) {
+        s->reduction_factor = avctx->lowres;
+    }
+    if (avctx->lowres != s->reduction_factor && avctx->lowres)
+        return AVERROR(EINVAL);
+
     ff_jpeg2000dsp_init(&s->dsp);
     ff_jpeg2000_init_tier1_luts();