title: scrapy spider is not starting start_requests function
body: <p>Scrapy script stops abruptly after the spider is inititialised before the call of start_requests function.
  I'm using Crawlrunner to initialise spider from a python script.</p>
  
  <p>python script :</p>
  
  <pre><code>custom_settings = { 'ITEM_PIPELINES' : { 'url_crawl.pipelines.UrlCrawlPipeline': 300}, 'COOKIES_ENABLED' : 'True', }
  runner = CrawlerRunner(custom_settings)
  
  @defer.inlineCallbacks
  def crwl():
      try:
          configure_logging({'LOG_FORMAT': '%(levelname)s: %(message)s'})
          lists = chunks(get_urls_to_crawl(), 30)
          for list in lists:
              print len(list)
              yield runner.crawl(UrlSpider, url_dict =list)
          d.addBoth(lambda _: reactor.stop()) #@UndefinedVariable
          reactor.run() #@UndefinedVariable
      except Exception as e:
          print e
  </code></pre>
  
  <p>and the spider looks like: </p>
  
  <pre><code>class UrlSpider(scrapy.Spider): 
      name = "url"  
      start_urls = [] 
  
      def __init__(self,url_dict):
          self.start_urls = []
          for url in url_dict:
              self.start_urls.append(url)
  
      def start_requests(self):
          user_agent = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.142 Safari/537.36'
          for url in self.start_urls:
              yield scrapy.Request(url = format(url[1]), headers={'User-Agent': user_agent,},callback=self.parse,meta = {'url':url[1],'id':url[0]})
  
      def parse(self, response):
          //////////////// extraction code //////////
  </code></pre>
  
  <p>the script stops abruptly after this log message:</p>
  
  <pre><code>2019-09-04 17:45:23 [scrapy.middleware] INFO: Enabled item pipelines:
  ['url_crawl.pipelines.UrlCrawlPipeline']
  2019-09-04 17:45:23 [scrapy.core.engine] INFO: Spider opened
  2019-09-04 17:45:23 [scrapy.extensions.logstats] INFO: Crawled 0 pages (at 0 pages/min), scraped 0 items (at 0 items/min)
  2019-09-04 17:45:23 [scrapy.extensions.telnet] INFO: Telnet console listening on 127.0.0.1:6023
  </code></pre>