Prevent RPC 'move' from deadlocking

It seemed to create two CWalletDB objects that both grab the
database lock.

src/wallet.cpp

@@ -291,10 +291,14 @@ bool CWallet::EncryptWallet(const SecureString& strWalletPassphrase)
     return true;
 }
 
-int64 CWallet::IncOrderPosNext()
+int64 CWallet::IncOrderPosNext(CWalletDB *pwalletdb)
 {
-    int64 nRet = nOrderPosNext;
-    CWalletDB(strWalletFile).WriteOrderPosNext(++nOrderPosNext);
+    int64 nRet = nOrderPosNext++;
+    if (pwalletdb) {
+        pwalletdb->WriteOrderPosNext(nOrderPosNext);
+    } else {
+        CWalletDB(strWalletFile).WriteOrderPosNext(nOrderPosNext);
+    }
     return nRet;
 }