Reduce inefficiency of GetAccountAddress()

Don't scan the wallet to see if the current key has been used if we're going to make a new key anyway.
Stop scanning the wallet as soon as we see that the current key has been used.
Don't call isValid() twice on the current key.

src/wallet/rpcwallet.cpp

@@ -137,26 +137,25 @@ CBitcoinAddress GetAccountAddress(string strAccount, bool bForceNew=false)
     CAccount account;
     walletdb.ReadAccount(strAccount, account);
 
-    bool bKeyUsed = false;
-
-    // Check if the current key has been used
-    if (account.vchPubKey.IsValid())
-    {
-        CScript scriptPubKey = GetScriptForDestination(account.vchPubKey.GetID());
-        for (map<uint256, CWalletTx>::iterator it = pwalletMain->mapWallet.begin();
-             it != pwalletMain->mapWallet.end() && account.vchPubKey.IsValid();
-             ++it)
-        {
-            const CWalletTx& wtx = (*it).second;
-            BOOST_FOREACH(const CTxOut& txout, wtx.vout)
-                if (txout.scriptPubKey == scriptPubKey)
-                    bKeyUsed = true;
+    if (!bForceNew) {
+        if (!account.vchPubKey.IsValid())
+            bForceNew = true;
+        else {
+            // Check if the current key has been used
+            CScript scriptPubKey = GetScriptForDestination(account.vchPubKey.GetID());
+            for (map<uint256, CWalletTx>::iterator it = pwalletMain->mapWallet.begin();
+                 it != pwalletMain->mapWallet.end() && account.vchPubKey.IsValid();
+                 ++it)
+                BOOST_FOREACH(const CTxOut& txout, (*it).second.vout)
+                    if (txout.scriptPubKey == scriptPubKey) {
+                        bForceNew = true;
+                        break;
+                    }
         }
     }
 
     // Generate a new key
-    if (!account.vchPubKey.IsValid() || bForceNew || bKeyUsed)
-    {
+    if (bForceNew) {
         if (!pwalletMain->GetKeyFromPool(account.vchPubKey))
             throw JSONRPCError(RPC_WALLET_KEYPOOL_RAN_OUT, "Error: Keypool ran out, please call keypoolrefill first");