fix: cookies setting in preNavigationHooks

[AndreyBykov]

This issue #1266 is kinda solved in the latest beta, but while testing I stuck upon an edge case when you try to set only one cookie (like mentioned in the issue), which leads to cookies array here having an actual cookie and a second item, which is gonna be an empty string, which is leading to:

TypeError: Cannot read properties of undefined (reading 'key')
      at /Users/AndreyBykov/Documents/Apify/Playground/playground/node_modules/apify/build/crawlers/crawler_utils.js:52:31
      at Array.find (<anonymous>)
      at mergeCookies (/Users/AndreyBykov/Documents/Apify/Playground/playground/node_modules/apify/build/crawlers/crawler_utils.js:51:62)
      at CheerioCrawler._mergeRequestCookieDiff (/Users/AndreyBykov/Documents/Apify/Playground/playground/node_modules/apify/build/crawlers/cheerio_crawler.js:570:87)
      at CheerioCrawler._handleNavigation (/Users/AndreyBykov/Documents/Apify/Playground/playground/node_modules/apify/build/crawlers/cheerio_crawler.js:540:14)
      at processTicksAndRejections (node:internal/process/task_queues:96:5)
      at async CheerioCrawler._handleRequestFunction (/Users/AndreyBykov/Documents/Apify/Playground/playground/node_modules/apify/build/crawlers/cheerio_crawler.js:475:9)
      at async wrap (/Users/AndreyBykov/Documents/Apify/Playground/playground/node_modules/@apify/timeout/index.js:73:27)

Closes #1266