Allow immediately executing RPC with no input

Story: https://tree.taiga.io/project/jktjkt-netconf-cli/us/189
Change-Id: I876437b798e995c4484e97b409117a2bb207e864
diff --git a/src/grammars.hpp b/src/grammars.hpp
index 02da179..2ff6e7a 100644
--- a/src/grammars.hpp
+++ b/src/grammars.hpp
@@ -259,10 +259,10 @@
 } const dump_args;
 
 auto const prepare_def =
-    prepare_::name > space_separator > rpcActionPath;
+    prepare_::name > space_separator > as<dataPath_>[RpcActionPath<AllowInput::Yes>{}];
 
 auto const exec_def =
-    exec_::name >> x3::attr(exec_{});
+    exec_::name > -(space_separator > as<dataPath_>[RpcActionPath<AllowInput::No>{}]);
 
 auto const cancel_def =
     cancel_::name >> x3::attr(cancel_{});