Maintain compatibility for forwarded RPC responses:

Typically, an RPC response contains a `result` field, which
contains details about the operation performed. For ease of
parsing, forwarded responses must look like a non-forwarded
response.

In some instances the response was incorrectly composed, so
that the actual `result` object would be encapsulated by an
outer `result` object, breaking existing code.

This commit, addresses this issue and correctly "folds" the
`result` field, ensuring a consistent schema for responses.

src/ripple/rpc/impl/ServerHandlerImp.cpp

@@ -904,6 +904,17 @@ ServerHandlerImp::processRequest(
             reply.append(std::move(r));
         else
             reply = std::move(r);
+
+        if (reply.isMember(jss::result) &&
+            reply[jss::result].isMember(jss::result))
+        {
+            reply = reply[jss::result];
+            if (reply.isMember(jss::status))
+            {
+                reply[jss::result][jss::status] = reply[jss::status];
+                reply.removeMember(jss::status);
+            }
+        }
     }
     auto response = to_string(reply);