rpcwallet: use EnsureWalletIsUnlocked() where possible

- replaces a pwalletMain->IsLocked() check
- in keypoolrefill init kpSize to 0 as we have the logic to determine max
  kpSize in pwalletMain->TopUpKeyPool() anyway

src/rpcwallet.cpp

@@ -334,8 +334,7 @@ Value sendtoaddress(const Array& params, bool fHelp)
     if (params.size() > 3 && params[3].type() != null_type && !params[3].get_str().empty())
         wtx.mapValue["to"]      = params[3].get_str();
 
-    if (pwalletMain->IsLocked())
-        throw JSONRPCError(RPC_WALLET_UNLOCK_NEEDED, "Error: Please enter the wallet passphrase with walletpassphrase first.");
+    EnsureWalletIsUnlocked();
 
     string strError = pwalletMain->SendMoneyToDestination(address.Get(), nAmount, wtx);
     if (strError != "")
@@ -1657,15 +1656,15 @@ Value keypoolrefill(const Array& params, bool fHelp)
             + HelpExampleRpc("keypoolrefill", "")
         );
 
-    unsigned int kpSize = max(GetArg("-keypool", 100), (int64_t) 0);
+    // 0 is interpreted by TopUpKeyPool() as the default keypool size given by -keypool
+    unsigned int kpSize = 0;
     if (params.size() > 0) {
         if (params[0].get_int() < 0)
-            throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid parameter, expected valid size");
+            throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid parameter, expected valid size.");
         kpSize = (unsigned int)params[0].get_int();
     }
 
     EnsureWalletIsUnlocked();
-
     pwalletMain->TopUpKeyPool(kpSize);
 
     if (pwalletMain->GetKeyPoolSize() < kpSize)