The issue has been raised by @florian.
Since D2007, the signrawtransaction RPC is routing the call to two new
RPCs, signrawtransactionwithkey and signrawtransactionwithwallet.
The routing is achieved by creating a copy of the JSON request and
forwading it to the new method.
The request URI is not copied during the process, which introduces a
regression when a node which uses multiple wallets calls
signrawtransaction: the request returns an error because the wallet is
This diff forwards the URI to the signrawtransactionwith* RPCs and
adds a test case to check the behavior.