Wallet/RPC: Use filename rather than CWallet pointer, for lockwallet

RPCRunLater job name

The job name is logged, and could pose as an information leak to someone
attacking the process, helping them counteract ASLR protections

src/wallet/rpcwallet.cpp

@@ -3427,7 +3427,7 @@ UniValue walletpassphrase(const JSONRPCRequest& request)
 
     if (nSleepTime > 0) {
         pwallet->nRelockTime = GetTime () + nSleepTime;
-        RPCRunLater ("lockwallet", std::bind (LockWallet, pwallet), nSleepTime);
+        RPCRunLater (strprintf("lockwallet(%s)", pwallet->GetName()), std::bind (LockWallet, pwallet), nSleepTime);
     }
 
     return NullUniValue;