GetSingleBlockByIndex does not work for new blocks in proxy mode

[nkcr]

In proxy mode, if I perform a GetSingleBlockByIndex for blocks that were not originally in the cached database, the result will fail.

[ineiti]

From what I see in the code, this is expected behaviour: https://github.com/dedis/cothority/blob/master/skipchain/skipchain.go#L695

If you want to change this behaviour, you'll need to open an issue and a PR against dedis/cothority...