Only return early from BlockUntilSyncedToCurrentChain if current tip

is exact match

In the next commit, we start using BlockConnected/BlockDisconnected
callbacks to establish tx depth, rather than querying the chain
directly.

Currently, BlockUntilSyncedToCurrentChain will return early if
the best block processed by the wallet is a descendant of the node'tip.
That means that in the case of a re-org, it won't wait for the
BlockDisconnected callbacks that have been enqueued during the re-org
but have not yet been triggered in the wallet.

Change BlockUntilSyncedToCurrentChain to only return early if the
wallet's m_last_block_processed matches the tip exactly. This ensures
that there are no BlockDisconnected or BlockConnected callbacks
in-flight.

Adaptation of btc@f77b1de16feee097a88e99d2ecdd4d84beb4f915

src/wallet/wallet.cpp

@@ -1363,12 +1363,9 @@ void CWallet::BlockUntilSyncedToCurrentChain() {
         uint256 last_block_hash = WITH_LOCK(cs_wallet, return m_last_block_processed);
         LOCK(cs_main);
         const CBlockIndex* initialChainTip = chainActive.Tip();
-
-        if (!last_block_hash.IsNull()) {
-            auto it = mapBlockIndex.find(last_block_hash);
-            if (it == mapBlockIndex.end() || it->second->GetAncestor(initialChainTip->nHeight) == initialChainTip) {
+        if (!last_block_hash.IsNull() && initialChainTip &&
+            last_block_hash == initialChainTip->GetBlockHash()) {
                 return;
-            }
         }
     }