Fix: block header times not being recorded correctly (#1605)

Whilst the delay was be calculated correctly the block time
that was recorded in the block header was not. This was leading to
problems with the time difference between blocks when using the timestamp
in the block header.

consensus/istanbul/qbft/core/request.go

@@ -57,11 +57,18 @@ func (c *core) handleRequest(request *Request) error {
 		delay := time.Duration(0)
 
 		block, ok := request.Proposal.(*types.Block)
+
 		if ok && len(block.Transactions()) == 0 { // if empty block
 			config := c.config.GetConfig(c.current.Sequence())
+
 			if config.EmptyBlockPeriod > config.BlockPeriod {
 				log.Info("EmptyBlockPeriod detected adding delay to request", "EmptyBlockPeriod", config.EmptyBlockPeriod, "BlockTime", block.Time())
+				// Because the seal has an additional delay on the block period you need to subtract it from the delay
 				delay = time.Duration(config.EmptyBlockPeriod-config.BlockPeriod) * time.Second
+				header := block.Header()
+				// Because the block period has already been added to the time we subtract it here
+				header.Time = header.Time + config.EmptyBlockPeriod - config.BlockPeriod
+				request.Proposal = block.WithSeal(header)
 			}
 		}