wallet: fix crash on double block disconnection

The wallet crashes if it processes the same block disconnection event twice in a row due
to an incompatible coinbase transaction state.
This happens because 'disconnectBlock' provides 'TxStateInactive' without the "abandoned"
flag for coinbase transactions to 'SyncTransaction', while 'AddToWallet()' internally
modifies it to retain the abandoned state.

The flow is as follows:
1) On the first disconnection, the transaction state transitions from "confirmed" to
"inactive," bypassing the state equality check since the provided state differs. Then,
'AddToWallet' internally updates the state to "inactive + abandoned"

2) On the second disconnection, as we provide only the "inactive" state
to 'SyncTransaction()', the state equality assertion fails and crashes the wallet.

Author: furszy

src/wallet/wallet.cpp

@@ -1548,8 +1548,11 @@ void CWallet::blockDisconnected(const interfaces::BlockInfo& block)
 
     int disconnect_height = block.height;
 
-    for (const CTransactionRef& ptx : Assert(block.data)->vtx) {
-        SyncTransaction(ptx, TxStateInactive{});
+    for (size_t index = 0; index < block.data->vtx.size(); index++) {
+        const CTransactionRef& ptx = Assert(block.data)->vtx[index];
+        // Coinbase transactions are not only inactive but also abandoned,
+        // meaning they should never be relayed standalone via the p2p protocol.
+        SyncTransaction(ptx, TxStateInactive{/*abandoned=*/index == 0});
 
         for (const CTxIn& tx_in : ptx->vin) {
             // No other wallet transactions conflicted with this transaction