logind: when creating the scope job fails, return this immediately to the client that wants to register the session

Otherwise we'll hanging for the job to finish without any job existing.

Similar, for machined.

src/login/logind-session.c

@@ -480,6 +480,7 @@ static int session_start_scope(Session *s) {
                         dbus_error_free(&error);
 
                         free(scope);
+                        return r;
                 } else {
                         s->scope = scope;
 

src/machine/machine.c

@@ -247,6 +247,7 @@ static int machine_start_scope(Machine *m) {
                         dbus_error_free(&error);
 
                         free(scope);
+                        return r;
                 } else {
                         m->scope = scope;