avcodec/mvha: Clear remaining space after inflate()

Fixes: use-of-uninitialized-value
Fixes: 70838/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MVHA_fuzzer-4878509466517504

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

libavcodec/mvha.c

@@ -183,6 +183,8 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *frame,
                     av_log(avctx, AV_LOG_ERROR, "Inflate error: %d\n", ret);
                     return AVERROR_EXTERNAL;
                 }
+                if (zstream->avail_out > 0)
+                    memset(zstream->next_out, 0, zstream->avail_out);
             }
         }
     } else if (type == MKTAG('H','U','F','Y')) {