title: Scrapy does not export all lines scraped to csv file
body: <p>I am very new to Scrapy and also Python. I tried to scrape products of two specific brands from this whisky website <a href="https://www.masterofmalt.com/distilleries-and-brands/" rel="nofollow noreferrer">https://www.masterofmalt.com/distilleries-and-brands/</a>.</p>
  
  <pre><code>import scrapy
  
  
  class WhiskyItem(scrapy.Item):
      name = scrapy.Field()
      country = scrapy.Field()
      region = scrapy.Field()
      distillery = scrapy.Field()
  
  class WhiskySpider(scrapy.Spider):
      name = "whisky_stack"
      start_urls = ['https://www.masterofmalt.com/distilleries-and-brands/']
  
      def parse(self, response):
          brands = response.xpath("//nav[@class='distillery-and-brands-list']/ul/li/a/@href").extract()
          for brand in brands:
              if brand == "https://www.masterofmalt.com/distilleries/the-macallan-whisky-distillery/" \
              or brand == "https://www.masterofmalt.com/distilleries/glenfarclas-whisky-distillery/":
                  yield scrapy.Request(brand, callback=self.parse_brands)
  
      def parse_brands(self, response):
          skus = response.css("div.product-box-wide").xpath("@data-product-url").extract()
          for sku in skus:
                  yield scrapy.Request(sku, callback=self.parse_sku)
          pages = response.css("nav.list-paging-wrapper a::attr(href)").extract()
          if pages is not None:
              pages = list(set(pages))
              for page in pages:
                  yield scrapy.Request(page, callback=self.parse_brands)
  
      def parse_sku(self, response):
          item = WhiskyItem() 
          item['name'] = response.xpath('//*[@id="ContentPlaceHolder1_pageH1"]/text()').extract()
          item['country'] = response.xpath('//*[@id="ContentPlaceHolder1_ctl00_ctl01_wdCountry"]/span[2]/a/text()').extract_first()
          item['region'] = response.xpath('//*[@id="ContentPlaceHolder1_ctl00_ctl01_wdRegion"]/span[2]/a/text()').extract_first()
          item['distillery'] = response.xpath('//*[@id="ContentPlaceHolder1_ctl00_ctl01_wdDistillery"]/span[2]/a/text()').extract_first()
          yield item
  </code></pre>
  
  <p>I can scrape all items from the website but the problem is that not all of them were exported to the csv file. Below is the command I use to export csv.</p>
  
  <pre><code>scrapy crawl whisky_stack -t csv -o whisky.csv
  </code></pre>
  
  <p>Is something going wrong here? Thanks!!!</p>