test: Add withdrawal-to-issuer assertion in IOU global-freeze test

Mirror the MPT and trust-line-freeze variants: under global freeze the
redemption path (dstAcct == vaultAsset.getIssuer()) should still succeed.

src/libxrpl/tx/transactors/vault/VaultWithdraw.cpp

@@ -283,7 +283,7 @@ VaultWithdraw::doApply()
     auto const freezeHandling =
         redeemingToIssuer ? FreezeHandling::IgnoreFreeze : FreezeHandling::ZeroIfFrozen;
 
-    // Share freeze checks are transitive. We skip them when withdrawing to the issuer all together.
+    // Share freeze checks are transitive. We skip them when withdrawing to the issuer alltogether.
     if (accountHolds(view(), accountID_, share, freezeHandling, AuthHandling::IgnoreAuth, j_) <
         sharesRedeemed)
     {

src/test/app/Vault_test.cpp

@@ -3538,6 +3538,11 @@ class Vault_test : public beast::unit_test::Suite
                 env(tx, Ter{tecFROZEN});
                 env.close();
 
+                // Withdrawal to the IOU issuer succeeds (redemption path)
+                tx[sfDestination] = issuer.human();
+                env(tx);
+                env.close();
+
                 // Cannot deposit some more
                 tx = vault.deposit({.depositor = owner, .id = keylet.key, .amount = asset(10)});