This fixes "Wallet file not specified" errors when making batch wallet RPC
calls with more than one wallet loaded. This issue was reported by
NicolasDorier <nicolas.dorier@gmail.com>
https://github.com/bitcoin/bitcoin/issues/11257
Request URI is not used for anything except multiwallet request dispatching, so
this change has no other effects.
Fixes #11257
Backport core's PR11277