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.

src/interfaces/chain.cpp

@@ -353,13 +353,11 @@ public:
     {
         return MakeUnique<NotificationsHandlerImpl>(*this, notifications);
     }
-    void waitForNotificationsIfNewBlocksConnected(const uint256& old_tip) override
+    void waitForNotificationsIfTipChanged(const uint256& old_tip) override
     {
         if (!old_tip.IsNull()) {
             LOCK(::cs_main);
             if (old_tip == ::ChainActive().Tip()->GetBlockHash()) return;
-            CBlockIndex* block = LookupBlockIndex(old_tip);
-            if (block && block->GetAncestor(::ChainActive().Height()) == ::ChainActive().Tip()) return;
         }
         SyncWithValidationInterfaceQueue();
     }

src/interfaces/chain.h

@@ -236,9 +236,8 @@ public:
     virtual std::unique_ptr<Handler> handleNotifications(Notifications& notifications) = 0;
 
     //! Wait for pending notifications to be processed unless block hash points to the current
-    //! chain tip, or to a possible descendant of the current chain tip that isn't currently
-    //! connected.
-    virtual void waitForNotificationsIfNewBlocksConnected(const uint256& old_tip) = 0;
+    //! chain tip.
+    virtual void waitForNotificationsIfTipChanged(const uint256& old_tip) = 0;
 
     //! Register handler for RPC. Command is not copied, so reference
     //! needs to remain valid until Handler is disconnected.

src/wallet/wallet.cpp

@@ -1113,7 +1113,7 @@ void CWallet::BlockUntilSyncedToCurrentChain() {
     // for the queue to drain enough to execute it (indicating we are caught up
     // at least with the time we entered this function).
     uint256 last_block_hash = WITH_LOCK(cs_wallet, return m_last_block_processed);
-    chain().waitForNotificationsIfNewBlocksConnected(last_block_hash);
+    chain().waitForNotificationsIfTipChanged(last_block_hash);
 }