fix: nil pointer

eth/fetcher/block_fetcher.go

@@ -422,7 +422,17 @@ func (f *BlockFetcher) loop() {
 
 		case op := <-f.requeue:
 			// Re-queue blocks that have not been written due to fork block competition
-			log.Info("Re-queue blocks", "number", op.header.Number.Int64(), "hash", op.header.Hash().String())
+			number := int64(0)
+			hash := ""
+			if op.header != nil {
+				number = op.header.Number.Int64()
+				hash = op.header.Hash().String()
+			} else if op.block != nil {
+				number = op.block.Number().Int64()
+				hash = op.block.Hash().String()
+			}
+
+			log.Info("Re-queue blocks", "number", number, "hash", hash)
 			f.enqueue(op.origin, op.header, op.block)
 
 		case op := <-f.inject: