Align trie iteration to substrate. (#90)

* Align trie iteration to substrate.

* Can use expect on trie error, remove debug_assert

cumulus/runtime/src/validate_block/implementation.rs

@@ -25,7 +25,7 @@ use sp_trie::{delta_trie_root, read_trie_value, Layout, MemoryDB};
 
 use hash_db::{HashDB, EMPTY_PREFIX};
 
-use trie_db::{Trie, TrieDB};
+use trie_db::{Trie, TrieDB, TrieDBIterator};
 
 use parachain::primitives::{HeadData, ValidationCode, ValidationParams, ValidationResult};
 
@@ -215,16 +215,8 @@ impl<B: BlockT> Storage for WitnessStorage<B> {
 			Err(_) => panic!(),
 		};
 
-		let mut iter = trie.iter().expect("Creates trie iterator");
-		iter.seek(prefix).expect("Seek trie iterator");
-
-		for x in iter {
+		for x in TrieDBIterator::new_prefixed(&trie, prefix).expect("Creates trie iterator") {
 			let (key, _) = x.expect("Iterating trie iterator");
-
-			if !key.starts_with(prefix) {
-				break;
-			}
-
 			self.overlay.insert(key, None);
 		}
 	}