Address #1538 and do not penalize peers for empty response. (#1811)

beacon_chain/request_manager.nim

@@ -89,6 +89,8 @@ proc fetchAncestorBlocksFromNetwork(rman: RequestManager,
           res = Result[void, BlockError].ok()
 
         if res.isOk():
+          if len(ublocks) > 0:
+            # We reward peer only if it returns something.
             peer.updateScore(PeerScoreGoodBlocks)
         else:
           # We are not penalizing other errors because of the reasons described