Fix nonsensical -norpcwhitelist behavior

Treat specifying -norpcwhitelist the same as not specifying -rpcwhitelist,
instead of behaving almost the same but flipping the default
-rpcwhitelistdefault value.

This is confusing because before this change if -norpcwhitelist was specified
it would block users from calling any RPC methods.

src/httprpc.cpp

@@ -334,7 +334,7 @@ static bool InitRPCAuthentication()
         }
     }
 
-    g_rpc_whitelist_default = gArgs.GetBoolArg("-rpcwhitelistdefault", gArgs.IsArgSet("-rpcwhitelist"));
+    g_rpc_whitelist_default = gArgs.GetBoolArg("-rpcwhitelistdefault", !gArgs.GetArgs("-rpcwhitelist").empty());
     for (const std::string& strRPCWhitelist : gArgs.GetArgs("-rpcwhitelist")) {
         auto pos = strRPCWhitelist.find(':');
         std::string strUser = strRPCWhitelist.substr(0, pos);