musig: Invalidate secnonce in partial_sign

Replace memset which can be optimized out.

Author: john-moffett

src/modules/musig/session_impl.h

@@ -677,9 +677,9 @@ int secp256k1_musig_partial_sign(const secp256k1_context* ctx, secp256k1_musig_p
     ARG_CHECK(secnonce != NULL);
     /* Fails if the magic doesn't match */
     ret = secp256k1_musig_secnonce_load(ctx, k, &pk, secnonce);
-    /* Set nonce to zero to avoid nonce reuse. This will cause subsequent calls
-     * of this function to fail */
-    memset(secnonce, 0, sizeof(*secnonce));
+    /* Clear and invalidate nonce to avoid nonce reuse. This will cause subsequent 
+     * calls of this function to fail */
+    secp256k1_musig_secnonce_invalidate(ctx, secnonce, 1);
     if (!ret) {
         secp256k1_musig_partial_sign_clear(&sk, k);
         return 0;