Add error message, if returned search HTML does not contain required elements

[phoehnel]

Change

This change adds a check, if the returned HTML from non-SERP scrapers like scraping robot or proxy contains the expected base structure.

This improves the problem from #272 where parsing fails on a bot-protection popup and returns position = 0.
The error that no results can be parsed on bot-protection still persists, but serpbear will show an error instead of dropping position to zero.

Behavior

• If the returned HTML is no valid search result: An error is raised
• If the returned HTML is valid, but the search has 0 results: Behavior unchanged - no Error and results = 0

Screenshot of changed version on error

Note, that the drop in the position graph was generated due to #272 and should not occur anymore with this change.

Log of changed version on error

serpbear  | [0] POST /api/refresh?id=5
serpbear  | [0] keywordIDs:  [ 5 ]
serpbear  | [0] START SCRAPE:  mykeword
serpbear  | [0] GET /api/keywords?domain=mydomain.de
serpbear  | [0] [ERROR] Scraped search results do not adhere to expected format. Unable to parse results
serpbear  | [0] [ERROR] Scraping Keyword :  mykeword
serpbear  | [0] [ERROR_MESSAGE]:  Error: [ERROR] Scraped search results do not adhere to expected format. Unable to parse results
serpbear  | [0]     at extractScrapedResult (/app/.next/server/chunks/941.js:322:15)
serpbear  | [0]     at scrapeKeywordFromGoogle (/app/.next/server/chunks/941.js:277:100)
serpbear  | [0]     at process.processTicksAndRejections (node:internal/process/task_queues:105:5)
serpbear  | [0]     at async refreshAndUpdateKeyword (/app/.next/server/chunks/941.js:79:34)
serpbear  | [0]     at async refreshAndUpdateKeywords (/app/.next/server/chunks/941.js:59:37)
serpbear  | [0] [SUCCESS] Updating the Keyword:  mykeword
serpbear  | [0] time taken: 2985.039358ms