demo-chains-sync: blockfetch demo is broken

I tried to run `blockfetch` demo and I noticed that the server is hitting an assertion exception:

```
cabal run demo-chain-sync -- blockfetch client +RTS -l -RTS
Up to date
[]
cur chain : (Origin,Origin)
demo-chain-sync: Assertion failed
CallStack (from HasCallStack):
assert, called at src/Ouroboros/Network/BlockFetch/State.hs:184:5 in ouroboros-network-0.1.0.0-inplace:
Ouroboros.Network.BlockFetch.State
CallStack (from -prof):
Ouroboros.Network.BlockFetch.State.fetchLogicIterations (src/Ouroboros/Network/BlockFetch/State.hs:(66,
1)-(83,24))
Ouroboros.Network.BlockFetch.blockFetchLogic (src/Ouroboros/Network/BlockFetch.hs:(237,1)-(293,29))
Control.Concurrent.Async.async (Control/Concurrent/Async.hs:194:1-35)
System.IOManager.withIOManager (src/System/IOManager.hs:63:1-51)
Main.clientBlockFetch (demo/chain-sync.hs:(251,1)-(394,74))
Main.main (demo/chain-sync.hs:(73,1)-(103,25))
```