avcodec/ivi: Clear got_p_frame before decoding a new frame using it

Fixes: assertion failure
Fixes: 21666/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_INDEO4_fuzzer-5706468994318336

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

libavcodec/ivi.c

@@ -1192,6 +1192,8 @@ int ff_ivi_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
             AVPacket pkt;
             pkt.data = avpkt->data + (get_bits_count(&ctx->gb) >> 3);
             pkt.size = get_bits_left(&ctx->gb) >> 3;
+            ctx->got_p_frame = 0;
+            av_frame_unref(ctx->p_frame);
             ff_ivi_decode_frame(avctx, ctx->p_frame, &ctx->got_p_frame, &pkt);
         }
     }