wallet: update stored witness in AddToWallet

Replace witness-stripped wallet transactions with full transactions;
this can happen when upgrading from a pre-segwit wallet to a segwit-
aware wallet.

src/wallet/wallet.cpp

@@ -914,6 +914,15 @@ bool CWallet::AddToWallet(const CWalletTx& wtxIn, bool fFlushOnClose)
             wtx.fFromMe = wtxIn.fFromMe;
             fUpdated = true;
         }
+        // If we have a witness-stripped version of this transaction, and we
+        // see a new version with a witness, then we must be upgrading a pre-segwit
+        // wallet.  Store the new version of the transaction with the witness,
+        // as the stripped-version must be invalid.
+        // TODO: Store all versions of the transaction, instead of just one.
+        if (wtxIn.tx->HasWitness() && !wtx.tx->HasWitness()) {
+            wtx.SetTx(wtxIn.tx);
+            fUpdated = true;
+        }
     }
 
     //// debug print