tools/target_dec_fuzzer: Free parser in case of avcodec_open2() failure

Fixes: memleak
Fixes: part of 15529/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_LIBVPX_VP8_fuzzer-5140143700180992

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

tools/target_dec_fuzzer.c

@@ -203,6 +203,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
     if (res < 0) {
         av_free(ctx);
         av_free(parser_avctx);
+        av_parser_close(parser);
         return 0; // Failure of avcodec_open2() does not imply that a issue was found
     }
     parser_avctx->codec_id = ctx->codec_id;