avcodec/hapdec: Clear tex buffer

The code following makes no attempt to initialize all of the buffer

Fixes: use of uninitialized value
Fixes: 70980/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HAP_fuzzer-5329909059223552

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

libavcodec/hapdec.c

@@ -310,6 +310,7 @@ static int hap_decode(AVCodecContext *avctx, AVFrame *frame,
             ret = av_reallocp(&ctx->tex_buf, ctx->tex_size);
             if (ret < 0)
                 return ret;
+            memset(ctx->tex_buf, 0, ctx->tex_size);
 
             avctx->execute2(avctx, decompress_chunks_thread, NULL,
                             ctx->chunk_results, ctx->chunk_count);