musig: VERIFY_CHECK preconditions of _musig_keyaggcoef_internal()

Author: real-or-random

src/modules/musig/keyagg_impl.h

@@ -166,6 +166,12 @@ static void secp256k1_musig_keyaggcoef_sha256(secp256k1_sha256 *sha) {
 static void secp256k1_musig_keyaggcoef_internal(secp256k1_scalar *r, const unsigned char *pk_hash, secp256k1_ge *pk, const secp256k1_ge *second_pk) {
     secp256k1_sha256 sha;
 
+    VERIFY_CHECK(!secp256k1_ge_is_infinity(pk));
+#ifdef VERIFY
+    VERIFY_CHECK(pk->x.normalized && pk->y.normalized);
+    VERIFY_CHECK(secp256k1_ge_is_infinity(second_pk) || (second_pk->x.normalized && second_pk->y.normalized));
+#endif
+
     if (!secp256k1_ge_is_infinity(second_pk)
           && secp256k1_fe_equal(&pk->x, &second_pk->x)
           && secp256k1_fe_is_odd(&pk->y) == secp256k1_fe_is_odd(&second_pk->y)) {