sort corpus when hitting genesis (#4470)

ethcore/src/client/traits.rs

@@ -220,6 +220,7 @@ pub trait BlockChainClient : Sync + Send {
 				let block = self.block(BlockId::Hash(h)).expect("h is either the best_block_hash or an ancestor; qed");
 				let header = block.header_view();
 				if header.number() == 0 {
+					corpus.sort();
 					return corpus;
 				}
 				block.transaction_views().iter().foreach(|t| corpus.push(t.gas_price()));

ethcore/src/tests/client.rs

@@ -233,6 +233,13 @@ fn empty_gas_price_histogram() {
 	assert!(client.gas_price_histogram(20, 5).is_none());
 }
 
+#[test]
+fn corpus_is_sorted() {
+	let client_result = generate_dummy_client_with_data(2, 1, slice_into![U256::from_str("11426908979").unwrap(), U256::from_str("50426908979").unwrap()]);
+	let client = client_result.reference();
+	let corpus = client.gas_price_corpus(20);
+	assert!(corpus[0] < corpus[1]);
+}
 
 #[test]
 fn can_handle_long_fork() {