don't attempt mempool entry for wallet transactions on startup if alr…

…eady in mempool

src/wallet/wallet.cpp

@@ -4323,6 +4323,11 @@ bool CWalletTx::IsInMainChainImmature() const
 
 bool CWalletTx::AcceptToMemoryPool(CValidationState& state, bool fLimitFree, bool fRejectInsaneFee, bool ignoreFees)
 {
+    // Quick check to avoid re-setting fInMempool to false
+    if (mempool.exists(tx->GetHash())) {
+        return false;
+    }
+
     // We must set fInMempool here - while it will be re-set to true by the
     // entered-mempool callback, if we did not there would be a race where a
     // user could call sendmoney in a loop and hit spurious out of funds errors