Merge bitcoin#25088: Wallet: Ensure m_attaching_chain is set before registering for signals

ba10b90 Wallet: Ensure m_attaching_chain is set before registering for signals (Luke Dashjr)

Pull request description:

  Avoids a race where chainStateFlushed could be called before rescanning began, yet rescan gets interrupted or fails

  Followup for bitcoin#24984 avoiding a race between registering and setting the flag.

ACKs for top commit:
  mzumsande:
    Code Review ACK ba10b90
  achow101:
    ACK ba10b90

Tree-SHA512: 1d2fa2db189d3e87f2d0863cf2ab62166094436483f0da16760b1083a4743bf08e476a3277e0d36564213d65dd6f0a1fc16a4bf68d3338c991a14d1de9fc0fee

Author: achow101

src/wallet/wallet.cpp

@@ -2964,6 +2964,7 @@ bool CWallet::AttachChain(const std::shared_ptr<CWallet>& walletInstance, interf
     // so that in case of a shutdown event, the rescan will be repeated at the next start.
     // This is temporary until rescan and notifications delivery are unified under same
     // interface.
+    walletInstance->m_attaching_chain = true; //ignores chainStateFlushed notifications
     walletInstance->m_chain_notifications_handler = walletInstance->chain().handleNotifications(walletInstance);
 
     // If rescan_required = true, rescan_height remains equal to 0
@@ -2990,7 +2991,6 @@ bool CWallet::AttachChain(const std::shared_ptr<CWallet>& walletInstance, interf
 
     if (tip_height && *tip_height != rescan_height)
     {
-        walletInstance->m_attaching_chain = true; //ignores chainStateFlushed notifications
         if (chain.havePruned()) {
             int block_height = *tip_height;
             while (block_height > 0 && chain.haveBlockOnDisk(block_height - 1) && rescan_height != block_height) {
@@ -3034,6 +3034,7 @@ bool CWallet::AttachChain(const std::shared_ptr<CWallet>& walletInstance, interf
         walletInstance->chainStateFlushed(chain.getTipLocator());
         walletInstance->GetDatabase().IncrementUpdateCounter();
     }
+    walletInstance->m_attaching_chain = false;
 
     return true;
 }