message: In `get_key_from_history` return None if the commit is not found
diff: @@ -468,12 +468,7 @@ impl IndexApi<TezedgeContext> for TezedgeIndex {
  let context_hash_arr: EntryHash = context_hash.as_ref().as_slice().try_into()?;
  match self.get_history(&context_hash_arr, key) {
  Err(MerkleError::ValueNotFound { key: _ }) => Ok(None),
  - Err(MerkleError::EntryNotFound { hash }) => {
  - Err(ContextError::UnknownContextHashAndEntryError {
  - context_hash: context_hash.to_base58_check(),
  - entry_hash: hash,
  - })
  - }
  + Err(MerkleError::EntryNotFound { hash: _ }) => Ok(None),
  Err(err) => Err(ContextError::MerkleStorageError { error: err }),
  Ok(val) => Ok(Some(val)),
  }
  