Fixes
$ ./src/test/fuzz/key_io ../btc_qa_assets/fuzz_seed_corpus/key_io
INFO: Seed: 2023332714
INFO: Loaded 1 modules (470791 inline 8-bit counters): 470791 [0x55d4f15d46e0, 0x55d4f16475e7),
INFO: Loaded 1 PC tables (470791 PCs): 470791 [0x55d4f16475e8,0x55d4f1d76658),
INFO: 203 files found in ../btc_qa_assets/fuzz_seed_corpus/key_io
INFO: -max_len is not provided; libFuzzer will not generate inputs larger than 4096 bytes
INFO: seed corpus: files: 203 min: 1b max: 465b total: 16482b rss: 99Mb
key.cpp:154:39: runtime error: null pointer passed as argument 1, which is declared to never be null
secp256k1/include/secp256k1.h:521:3: note: nonnull attribute specified here
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior key.cpp:154:39 in
