Fix treasury kept and spend when emptied (#3880)

* Now construct_runtime must include treasury config so account is created at genesis.
* if it doesn't though it is ok, account will be created when the amount put is more than existential deposit.

substrate/node/testing/src/genesis.rs

@@ -96,5 +96,6 @@ pub fn config(support_changes_trie: bool, code: Option<&[u8]>) -> GenesisConfig
 		membership_Instance1: Some(Default::default()),
 		elections_phragmen: Some(Default::default()),
 		sudo: Some(Default::default()),
+		treasury: Some(Default::default()),
 	}
 }