Skip indexing if a page has not changed (see contao#2250)

Description
-----------

| Q                | A
| -----------------| ---
| Fixed issues     | Fixes contao#2235
| Docs PR or issue | -

Same as contao#2249 but for Contao 4.10.

Commits
-------

b669725 Skip indexing if page has not changed
200a704 Fix SQL
c07379c CS
e3310bb Do not cast do boolean
8f00bfb Merge branch '4.10' into fix/search-early-return

core-bundle/src/Resources/contao/library/Contao/Search.php

@@ -177,6 +177,17 @@ public static function indexPage($arrData)
 		// Calculate the checksum
 		$arrSet['checksum'] = md5($arrSet['text']);
 
+		$blnIndexExists = $objDatabase
+			->prepare("SELECT EXISTS(SELECT id FROM tl_search WHERE checksum=? AND pid=? AND url=?) as indexExists")
+			->execute($arrSet['checksum'], $arrSet['pid'], $arrSet['url'])
+			->indexExists;
+
+		// The page has already been indexed and has not changed (see #2235)
+		if ($blnIndexExists)
+		{
+			return false;
+		}
+
 		// Prevent deadlocks
 		$objDatabase->query("LOCK TABLES tl_search WRITE, tl_search_index WRITE, tl_search_term WRITE");