perf: generate_initial_session_keys: load runtime only if its relevant (#12651)

* perf: generate_initial_session_keys: load runtime only if its relevant

* apply review suggestion

* Update primitives/session/src/lib.rs

Co-authored-by: Bastian Köcher <git@kchr.de>

Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/primitives/session/src/lib.rs

@@ -118,6 +118,10 @@ where
 	T: ProvideRuntimeApi<Block>,
 	T::Api: SessionKeys<Block>,
 {
+	if seeds.is_empty() {
+		return Ok(())
+	}
+
 	let runtime_api = client.runtime_api();
 
 	for seed in seeds {