[process] Fix a very nasty bug in processing messages

In some cases, we could have forgotten to parse the incoming message. We would have 2x messages in the TCP stream, we would consume the first one but forgot about the second one

process/controller/src/remote.cpp

@@ -199,7 +199,7 @@ namespace praas::process::remote {
       // Three types of messages require long payloads:
       // invoke
       // put
-      std::visit(
+      consumed = std::visit(
           common::message::overloaded{
               [this, buffer, conn = conn.get()](common::message::InvocationRequestPtr& invoc
               ) mutable -> bool { return _handle_invocation(*conn, invoc, buffer); },