Merge bitcoin#15299: Fix assertion in CKey::SignCompact

3617f11 Fix assertion in CKey::SignCompact (João Barbosa)

Pull request description:

  Fixes bitcoin#15286.

Tree-SHA512: b39b6f26f87cf1850b13f625ab6de963937b6ecb5b6d4ac4932134f0491a6c0fa61c6d6e6980e8b1770775578dc365fdd1b6ba426bba1f7c23430f68b3a2339a

Author: laanwj

src/key.cpp

@@ -246,7 +246,7 @@ bool CKey::SignCompact(const uint256 &hash, std::vector<unsigned char>& vchSig)
     secp256k1_ecdsa_recoverable_signature sig;
     int ret = secp256k1_ecdsa_sign_recoverable(secp256k1_context_sign, &sig, hash.begin(), begin(), secp256k1_nonce_function_rfc6979, nullptr);
     assert(ret);
-    secp256k1_ecdsa_recoverable_signature_serialize_compact(secp256k1_context_sign, &vchSig[1], &rec, &sig);
+    ret = secp256k1_ecdsa_recoverable_signature_serialize_compact(secp256k1_context_sign, &vchSig[1], &rec, &sig);
     assert(ret);
     assert(rec != -1);
     vchSig[0] = 27 + rec + (fCompressed ? 4 : 0);